COLUMN ONE : Cold War Foes Forge Warm Ties : What once was called treason is now encouraged by the U.S. and Russia. Former bomb rivals share expertise as Americans help reduce Soviet arsenal and keep Moscow’s arms experts busy.

On arid mesas in northern New Mexico, screened by stands of ponderosa pine and rolls of concertina wire, generations of American physicists, chemists and engineers created the most destructive weapons ever built.

In 50 years of nuclear stalemate, these secluded Cold Warriors rarely came face to face with their most accomplished adversaries--the men and women who built the Soviet thermonuclear weapons aimed until recently at American cities.

With few exceptions, the names of those Soviet scientists were state secrets, their faces unknown outside cloistered military laboratories. Even the cities where they lived and labored were stricken from official maps.

Now, after the collapse of the Soviet Union, American weapons experts are quietly collaborating in dozens of non-military research projects in Russia and the United States with the bomb makers they tried so implacably to thwart.

Divided for decades by ideology and national security barriers, American and Russian nuclear weapons experts have been brought together by the need to control the intractable technology of destruction they nurtured and perfected.

If security guards are startled to see Russian scientists toiling in the warrens of Los Alamos, it is no more disconcerting than to find U.S. physicists testing a fusion reactor inside the fences of Arzamas-16, site of the once-secret Soviet weapons lab that developed Russia’s hydrogen bomb.

“There continues for all of us to be an element of disbelief,” said Los Alamos physicist Irvin R. Lindemith, who has been exploring the frontiers of fusion energy with Russian weapons scientists.

“We are doing things that might have been impossible,” he said, “or been reason to suspect treason.”

The joint research between U.S. and Russian weapons scientists is at the emotional center of an unprecedented effort by Western governments and private philanthropists to dismantle most of the nuclear weapons in the former Soviet Union, while keeping thousands of scientists gainfully employed throughout Russia, Ukraine, Belarus and other independent states.

As a matter of American national security, some scientists at Los Alamos and other U.S. national laboratories also are doing their best to keep the Russian weapons scientists busy with civilian work.

Although superpower hostilities may have eased, the secrecy and security precautions surrounding almost every aspect of each country’s nuclear stockpile are as stringent as ever. Aiding the Russians poses its own special security dilemmas, however, Los Alamos weapons experts and State Department officials said.

U.S. officials must balance the danger of funding scientists still actively involved in nuclear weapons programs against the possibility that those researchers can be persuaded to pursue more peaceful careers.

Russian authorities, on the other hand, must worry whether the joint projects are attempts at espionage masquerading as charity or, worse, efforts designed to cripple the Russian defense industry by sapping its creative talent.

“There is always the fear that an American offer of help in conversion of military scientists is a hidden effort to keep Russia weak . . . to make sure Russia does not ever build up its power again,” said Loren R. Graham, a Massachusetts Institute of Technology authority on science in Russia and the Soviet Union.

In reaching out to the Russians, researchers at Los Alamos not only are helping their former adversaries, they are creating a new role for themselves as custodians of the nuclear danger they created.

Weapons experts from the Los Alamos, Lawrence Livermore and Sandia national laboratories have become globe-trotting diplomats who try to limit the spread of nuclear weapons in South Africa, Brazil, North Korea, Iraq, Iran and, most recently, China.

Their travel orders today are more likely to take them to secret weapons facilities in Ukraine or in Russia than to the Nevada Test Site, where until 1992 the United States routinely tested experimental nuclear weapons.

“This has redefined a national mission for the weapons labs,” said Anne Harrington, who coordinates nuclear non-proliferation programs at the State Department.

“It is not just helping the Russians to find something useful and civilian to do,” she said of the nuclear diplomacy. “It is also helping the labs here to do the same thing.”

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No one knows how many people worked in the Soviet nuclear weapons complex, and, until last year, no one was sure how many nuclear arms the Soviet Union had deployed across its vast territories.

Congressional experts and intelligence sources today say that at the peak of its power the Soviet Union had almost 45,000 warheads--12,000 more than anyone had guessed. Its stores of bomb-grade uranium were nearly 1,200 tons--more than twice as much as formerly thought, congressional experts said.

The nuclear warheads, weapons-grade materials and the expertise of bomb builders in the former Soviet Union continue to pose the most immediate danger. Although treaties officially limit the spread of nuclear weapons, there are five declared nuclear powers and at least 20 countries have tried covertly to develop them, Defense Department security experts say. The Russian storehouse presents a tempting way to realize their nuclear ambitions.

Since 1991, there have been 50 reported incidents of nuclear materials being smuggled from Russia, but until recently most involved non-weapons materials, experts said. During the past year, however, authorities announced five major cases of nuclear smuggling from Russia, with some evidence that the materials were diverted from poorly guarded weapons facilities.

Efforts to infiltrate the federal Nuclear Research Center in the closed city of Arzamas-16 near Moscow reportedly have doubled in the past year, Russian security officials recently announced.

While Russian authorities insist no weapons material has been stolen, Robert E. Kelley, who manages the Los Alamos proliferation response program, says the kind of nuclear material showing up on the black market recently has taken a disturbing turn.

“In the last six months, the [black market] nuclear material is different. It is weapons material,” Kelley said. “It is directly usable [in a weapon] in its present form.”

Specialists at Los Alamos and other U.S. national laboratories are trying to make Russia a safer and more sophisticated nuclear power. To help secure its scattered nuclear arsenal, they are acquainting Russians with computerized inventory controls and electronic security measures.

As warheads are shipped back to Russia from bases in Ukraine or Kazakhstan and Belarus, they are bundled in American-made blankets of bulletproof Kevlar to protect them from rifle fire along the route. They are cradled in rail cars refitted by the United States to carry nuclear materials. The bombs are being laid to rest in shelters U.S. scientists are helping to design.

In the event of an accident, Russian emergency teams trained at Los Alamos would use U.S. radiation-monitoring equipment, protective clothing and mobile X-ray equipment to examine damaged warheads.

And if they needed to dismantle a nuclear weapon at a disaster site, they probably would use special U.S. devices that can slice up a warhead without causing the sparks that could set off its high-explosive detonator.

U.S. officials have been especially eager to ensure that the Russians most knowledgeable about nuclear operations--often unemployed, unappreciated or unpaid in the economic chaos after the dissolution of the Soviet government--do not sell their expertise to countries trying to build their own arsenals.

Indeed, Russian officials recently threatened to expel North Korean diplomats if they did not stop trying to recruit former Soviet weapons specialists.

Earlier this month, scientists and workers at the Federal Nuclear Research Center in Arzamas-16 staged several days of protests when they abruptly were reduced to a poverty allowance, in lieu of salaries that had gone unpaid for months. Tass, the Russian news agency, reported that tensions were “explosive.”

It was only the most recent in a series of incidents spurred by the anemic economy and the breakdown of organization within the Russian weapons complex.

Kimberly Marten Zisk, a Russian expert at Ohio State University, recently discovered an unusual archive in Moscow of community newspapers from Arzamas-16. The documents reveal that scientists at Russia’s most prestigious nuclear weapons laboratory, once a pampered elite, are now struggling to survive and adapt.

Lab administrators cannot even pay the water or sewer bills, while salaries are so uncertain that many scientists support their families by raising food in garden plots.

Last year, directors of the weapons plant in Arzamas-16 were so angry about unpaid salaries and worsening conditions in the closed city that they warned in an open letter of “unpredictable consequences” unless the government paid the workers and provided more financial support.

Plant officials were so concerned that disgruntled workers might carelessly or deliberately sabotage efforts to dismantle weapons that the center suspended dangerous work until salaries had been paid.

“We are worried about idle hands and empty pockets looking elsewhere,” said Glenn Schweitzer, an expert on Russia and Central Europe at the National Science Foundation who helped organize a research center in Moscow to fund peaceful projects by former weapons scientists.

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In the community of Los Alamos, nestled at the beginning of the crooked road that leads from the place where the atomic bomb was invented 50 years ago, reaching out to Russian weapons experts is a personal matter.

Even before glasnost, lab scientists quietly nurtured informal relationships with their Soviet counterparts. Once the Soviet government collapsed in 1991, laboratory experts often rushed ahead of formal government policy-makers to open the closed Soviet laboratories.

They made their own plans first and sought official permission later, State Department and lab officials said. They arranged at least one major nuclear non-proliferation project in a series of informal, weekend telephone calls to Russia.

David Holloway, a Stanford University expert on the Soviet nuclear weapons program and author of “Stalin and the Bomb,” said Russian scientists were eager to have their skills acknowledged by U.S. weapons experts. That helped researchers at Los Alamos and other national laboratories open doors closed to Western diplomats.

“In the early days our government was not exactly enthusiastic about these interactions,” said Stephen M. Younger, director of the Los Alamos Center for International Security Affairs.

“We decided we were not going to ask permission,” he said.

As the principal contact for the Soviet weapons designers, he has visited Arzamas-16 a dozen times since 1992 as part of U.S. negotiating teams or to participate in joint projects--more often than anyone without a Russian secret clearance.

Younger recalls with relish how he warmed his hands in the frigid air of Arzamas-16 with a piece of copper shrapnel still glowing from the explosion of an experimental fusion device. He tells with even more satisfaction how, a few months later, Russian scientists traveled from Arzamas-16 to the arroyos above Los Alamos to test a high-explosive fusion reactor, similar to the implosion devices that trigger a nuclear warhead.

“We fired the first Russian implosion device on U.S. soil,” he said. “It was delivered by Federal Express, not by an SS-19 [missile].”

In the past three years, Los Alamos and Arzamas-16 have become sister cities and their citizens have pen pals. They have sponsored exchange visits of high school students. This spring, a delegation of local politicians and Chamber of Commerce officials visited the Russian enclave.

Los Alamos citizens even raised $500,000 to buy medicine for the children of the beleaguered weapons laboratory.

But most arms control experts say such goodwill gestures are not a long-term solution to the problem of nuclear weapons.

Measured against the scale of Cold War defense spending, the U.S. effort to safely retrieve and dismantle Soviet nuclear weapons is modest and the official attempts to aid former Soviet scientists are grudging, U.S. officials acknowledge.

At the Los Alamos laboratory, which employs 11,000 people, no more than 20 scientists have been working full time on the project at any one time. Much of its joint research has been paid out of discretionary funds.

The linchpin of the official U.S. effort with Russian scientists is the Pentagon-funded International Science and Technology Center in Moscow. Since opening last year, it has spent a modest $60 million to fund 130 three-year research projects involving 8,200 Russian weapons scientists. A similar center has been opened in Ukraine.

In all, the Defense Department has budgeted a total of $1.3 billion over five years for the disarmament projects--barely equal to the cost of a strategic antiballistic missile warning radar installation the U.S. Air Force recently closed.

Of that, U.S. officials have spent only $177 million since 1991.

Red tape, political unrest, severe security constraints and diplomatic protocol have slowed the pace of the collaboration to a crawl.

In the past three years, planning for a warhead storehouse has bogged down. Pentagon inaction has allowed $330 million in funding to lapse unused. U.S. officials have yet to implement a landmark agreement to buy processed Russian uranium containing 500 tons of weapons-grade plutonium.

And only after a philanthropist agreed to match the funds this spring did the Pentagon allocate $5 million to open a new Civilian Research and Development Foundation in Moscow.

“It has taken a long time to get a little bit done,” said Steven J. Gitomer, a Los Alamos researcher who is serving as science adviser to the Moscow-based science center.

The most daunting challenges are still ahead. By 2003, Russia and the United States are expected to have scrapped two-thirds of their deadliest weapons, reducing the number of long-range warheads they each hold to 3,000 to 5,000.

Researchers acknowledge that they are not really sure yet how best to break a nuclear weapon into its smallest, safest and least classified components for safe storage during the centuries it will remain lethal.

Nor is there any lasting way to neutralize the dangerous knowledge U.S. and Russian scientists have acquired.

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In many ways, scientists at Los Alamos and Arzamas-16 remain prisoners of their work.

Even as some security restrictions are relaxed, the nature of their scientific knowledge continues to place them in a world apart.

While researchers at Arzamas-16 still are isolated physically--cut off by security zones and travel restrictions--the people of Los Alamos are isolated by politics, anti-nuclear sentiments and revulsion within some parts of the scientific community for their role as the catalyst for decades of nuclear brinkmanship.

Many researchers believed fervently in the strength of the nuclear shield they erected over their homeland. Others were motivated by the desire to pursue experiments that could only be funded as weapons work. Some have spent their professional lives in private torment--caught in the tension caused by the uneasy morality of nuclear weapons work, the desire to maintain peace, and the scientific exhilaration of unleashing nature’s most powerful energies.

At the Los Alamos museum dedicated to the laboratory’s technical and military achievements, there is a corner reserved for remorse.

There hang photographs of the architects of the first atomic bomb--physicists such as Nobel laureates Hans Bethe and I.I. Rabi, among the most important scientists of the 20th Century--with their statements of regret over what they unleashed.

With them is a black-and-white photograph of physicist Robert Oppenheimer, who is memorialized as the scientist who oversaw the Manhattan Project and the invention of nuclear weapons.

Next to it is his own judgment on what they did together: “In some sort of crude sense, which no vulgarity, no humor, no overstatement can quite extinguish, the physicists have known sin, and this is a knowledge which they cannot lose.”

There is an equally strong undercurrent of emotion among some of the weapons scientists working with the Russians. They are experiencing a euphoria that in part may be the lifting of a burden of conscience.

“I used to do nuclear weapons design,” said Stephen Younger, who now coordinates the Los Alamos laboratory’s efforts to cooperate with Russian weapons scientists.

“When you walk up to a crater that is 1,000 feet across and 50 feet deep and you know that was caused by something you held in your hand a few weeks before, you have a good appreciation of nuclear weapons,” he said.

“If we can turn the nuclear weapons programs of both countries from designing weapons that we point against one another to working together on fundamental science, I think our children’s children will call us blessed.”

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HOW TO DISARM A SUPERPOWER

Efforts to dismantle the nuclear weapons of the former Soviet Union are complicated because the government responsible for building and deploying them no longer exists. U.S. weapons experts are helping Russia, which has taken legal custody of the weapons. The process goes something like this: FIRST--The bombs stationed in what are now separate countries have to be retrieved. The Soviet Union had about 27,000 nuclear weapons in 1991. By next February, Belarus, Ukraine and Kazakhstan are expected to be nuclear free.

* Belarus--An estimated 36 single-warhead mobile strategic missiles remain.

* Ukraine--More than 700 warheads have been removed. Of those, about 420 have been returned to Russia.

* Russia--Strategic missiles are no longer targeted at the United States.

* Kazakhstan--By April, all warheads had been returned to Russia. SECOND--Weapons-grade materials have to be stored securely.

* U.S. has supplied computerized inventory systems and electronic security to protect weapons materials. THIRD--The scientists who designed nuclear weapons should find civilian work.

* More than 8,200 Russian weapons scientists are now working on U.S.-funded, non-military research projects.

FOURTH--Weapons laboratories should be turned into non-military research centers.

* Russian labs are now working with 180 U.S. industrial partners. Sources: Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Carnegie Endowment for International Peace, Congressional Research Service, Bulletin of Atomic Scientists