NEWS ANALYSIS : Gorbachev Out Front on Disarmament : Weapons: Three key proposals reflect the Soviet leader’s commitment to a world free of nuclear arsenals.

Mikhail S. Gorbachev proved to be more than ready this weekend for President Bush’s challenge to reduce the two superpowers’ nuclear arsenals.

Like the U.S. President, the Soviet leader knew there were weapons--first of all, short-range, tactical nuclear weapons--that had not only outlived their Cold War usefulness but were now decidedly dangerous to the Soviet Union itself as the country fragments into perhaps a dozen independent nations.

And Gorbachev, like Bush, had other cuts he wanted to make, notably a 700,000-man reduction in the overall strength of the massive Soviet armed forces, and the need to match the U.S. initiative was a good occasion to announce them.

But at the core of Gorbachev’s response to Bush’s initiative are three key disarmament proposals that reflect his commitment to a world free of nuclear weapons:

* A 50%, across-the-board reduction in the two superpowers’ strategic nuclear arsenals, quickly cutting them back to 3,000 warheads each. As a goodwill gesture, Gorbachev announced a unilateral 1,000-warhead cutback in the Soviet nuclear forces.

* An end to nuclear testing as a way to halt the modernization of nuclear weapons. Gorbachev announced an immediate one-year ban on Soviet tests.

* A pledge not to be the first to use nuclear weapons in a conflict, a commitment that would cut across NATO’s threat of U.S. nuclear retaliation if the Soviet Union attacked Europe with conventional forces.

After matching the Bush proposals virtually point for point, Gorbachev took the initiative significantly further in an effort to set the focus of a new round of Soviet-American arms reduction negotiations.

“We have a number of proposals transcending the framework of the proposals made by the American side, and in this respect Gorbachev has gone further than Bush,” Alexei Obukhov, a deputy Soviet foreign minister, said Sunday as exploratory talks opened here with a U.S. delegation led by Reginald Bartholomew, undersecretary of state for international security affairs.

“Both packages on the whole . . . have given rise to a qualitatively new situation in the field of nuclear disarmament,” Obukhov commented. “This situation is very favorable for making important new decisions, and in this sense I believe we are experiencing quite a new period in world politics.”

Soviet arms-control specialists, while praising how quickly Bush’s unilateral initiatives dealt with the issue of tactical nuclear weapons, said last week that the primary impulse for nuclear disarmament would still have to come through negotiations.

Although they were dismayed at the decade it took to conclude the Strategic Arms Reduction Treaty that Bush and Gorbachev signed here two months ago, they stressed the need to maintain an overall balance in the nuclear arsenals and to avoid what one called an “inherent volatility” of unilateral cuts.

“We need the mutual assurance of negotiated reductions,” one Kremlin arms-control adviser said, asking not to be quoted by name. “The Americans want to ‘lock in’ their gains and to avoid ‘breakout’ violations, and we want to ‘cap’ their U.S. inventiveness. All this realistically requires negotiations and treaties.

“There is also a political factor for us--our generals need to be involved in the negotiations and need to know our security will not be diminished. And the coup in August was a reminder that our military still is uncertain about reform or a return to the past. We need negotiated, balanced treaties.”

Where Bush called for the elimination of land-based intercontinental ballistic missiles with multiple warheads--potential first-strike weapons that are the leading element in the Soviet arsenal--Gorbachev consequently proposed far broader cuts that would maintain a balance of power at reduced levels that would require cutbacks in the U.S. submarine and bomber forces.

Gorbachev, given an opening by Bush, was putting into practice the new Soviet strategic doctrine of “reasonable sufficiency,” that is, having enough to defend the country but no more.

The new Soviet military leadership emphasizes not the number of warheads and weapons but flexibility, mobility and survivability. What Moscow needs, according to the new defense thinking, is not the massive nuclear strike force and deterrent of the past but “minimum residual strength.”

An important inducement for the United States, according to some arms-control specialists here, is the first Soviet willingness to accept at least elements of “Star Wars,” the U.S. Strategic Defense Initiative against missile attack.

Although Moscow had long opposed it as another step in the arms race and a violation of the U.S.-Soviet treaty on ballistic-missile defenses, Gorbachev expressed interest in a joint monitoring system that would offer protection against attack by other countries.

Known as “global protection against limited strikes,” a scaled-down U.S. plan would defend against only 100 to 200 missiles, not the thousands as first proposed, and recognize that the greater threat comes from the proliferation of ballistic missiles in the Third World, not from a superpower confrontation.

“We are definitely interested but only on the condition, as President Reagan first proposed, of shared technology,” a science adviser to Gorbachev said last week. “The issue is balance and stability in the balance.

“We don’t want this ‘rush to disarm,’ as our commentators are calling it, to upset what we have achieved. ‘Seize the day,’ yes, but not at the cost of destabilizing the international situation.”

Another Soviet goal, according to arms control sources here, is the inclusion of other nuclear powers--Britain, China and France--once the United States and the Soviet Union have reduced their arsenals to the proposed 3,000 warheads each.

Andrei S. Grachev, Gorbachev’s press secretary and one of the country’s top strategic thinkers, argued last week that the Soviet Union, despite all the skepticism in the West, remains motivated by the goal of a world free from nuclear weapons by the year 2000.

“Yes, you can laugh and say, ‘impossible, unrealistic, unachievable,’ ” Grachev said, commenting on Bush’s initiative. “But is this not simply a cynical refusal to try? Who needs these weapons today? Why not work for ways to eliminate them?

“This is what has motivated the Soviet Union since President Gorbachev first made his nuclear-free proposal five years ago, and I think we can see in the Bush initiative a response that is just as historical in its import.”

In the toughest Soviet appraisals, however, the Bush initiative appeared to have two goals--scoring gains while Gorbachev and the Soviet Union as a whole were preoccupied with the country’s political and economic crisis and helping Gorbachev eliminate tactical nuclear weapons from the Soviet arsenal lest they fall into the hands of mutinous troops or the country’s breakaway republics.

In an acerbic commentary, the Communist Party newspaper Pravda last week summed up Bush’s motive as simply, “Get things done while Gorbachev is here.”