Arms Reduction Treaty Unlikely to Be Finished by End of Bush’s Term : Defense: Nuclear weapons agreement is slowed by Russian requests for changes.

The second Strategic Arms Reduction Treaty--which would cut nuclear weapons and which once was hailed by President Bush as a major achievement of his Administration’s diplomacy--is unlikely to be completed by the time Bush leaves office because of Russian misgivings and American uncertainty, officials said this week.

Russia has asked for several changes in the basic framework for a new agreement that Bush and Russian President Boris N. Yeltsin announced in June. But the issues are so complex that the two sides have been unable to resolve their differences, senior officials said.

“I’m doubtful that it can be wrapped up in the next 60 days,” said one official involved in the negotiations. “I don’t know. Maybe it can. . . . But it is a complicated bloody thing.”

Arms control experts said the Russians and the Bush Administration both are partly responsible for the failure to finish the agreement. The Russians were slow in proposing their amendments and responding to American questions, they said.

Meanwhile, Bush and former Secretary of State James A. Baker III devoted their attention to the presidential campaign and did not have time to launch a high-level negotiating effort.

Still, the deliberate pace of the talks has alarmed some arms control advocates, who fear that the agreement could evaporate if it is not concluded soon.

“This is . . . one of those items that the Bush Administration should try to negotiate while they’re in office, if possible,” Sen. Richard G. Lugar (R-Ind.) said. He noted that, if Bush does not complete the agreement, President-elect Bill Clinton is unlikely to do so before his new Administration is fully in place in April or May.

“We do have problems, if we go past the inauguration,” a State Department official acknowledged. “Once you have a new Administration, you have to sit down and go through all the numbers again. You risk reopening some old arguments. And, if nothing else, you’ve lost time.”

Indeed, on the day after his election Nov. 3, Clinton publicly offered his support for Bush’s efforts to complete the negotiations--a veiled appeal to both sides to wrap the agreement up before Inauguration Day.

At the same time, there is a political dilemma on the Russian side: Yeltsin faces a potentially stormy session, starting Tuesday, of the Congress of People’s Deputies, the Parliament dominated by his former Communist critics. Some U.S. officials believe that the Russian president does not want to compromise with Bush over the fine print of START 2 at a time when he is already fighting off criticism from hard-liners on other issues.

The agreement, which Bush and Yeltsin announced at their summit meeting here in June, would build on the already-concluded START 1 agreement to slash the U.S. and Russian nuclear arsenals from more than 11,000 long-range warheads on each side to fewer than 3,500 each, the lowest levels in two decades. Equally important, it commits both nuclear powers to eliminate missiles which carry multiple warheads, the most dangerous nuclear weapons.

After the two presidents reached the agreement, however, officers in Russia’s armed forces expressed misgivings about the deal, which would eliminate the core of the Kremlin’s nuclear weaponry. With the details of the pact still under negotiation, Russia asked for several significant amendments.

“No one is walking away from the agreement . . . and no one is saying that these issues are matters of principle that would affect the national security of Russia or the United States,” a senior official said. “But these are still serious, complex matters.”

The Russians have raised four major issues, arms control experts said:

* Downloading. The Russians’ most controversial proposal is a request to keep their SS-19 multiple-warhead missiles but to comply with the agreement by removing all but one warhead--an arrangement that would save the Russians billions of rubles. American officials have objected that this arrangement, known as “downloading,” would be difficult to verify, because it would be hard to make sure that the other warheads stayed off.

* Silos. The Russians have agreed to destroy all their giant SS-18 missiles, but they then asked for permission to use the hardened silos that housed the SS-18s for other, single-warhead missiles. The two countries appear to be working toward a compromise that would allow the Russians to use the silos but assure the United States that no SS-18s remain.

* Bombers. The Russians have asked for more detailed rules to govern the use of U.S. Air Force long-range bombers. Under the agreement, the United States can declare that some bombers are not carrying nuclear weapons, making them exempt from START 2. The Russians want more reassurance that the non-nuclear bombers cannot be converted quickly into nuclear bombers.

* The ABM Treaty. The Russians asked for an explicit reaffirmation of the 1972 Anti-Ballistic Missile Treaty, which restricts each country’s ability to deploy weapons to defend against incoming nuclear missiles. (For example, the treaty would prohibit the United States from deploying the kind of defensive systems that the Strategic Defense Initiative has been trying to develop.) The Bush Administration has agreed to this request.

Administration officials point out that by historical standards, the START 2 negotiations have occurred at breakneck speed. “This kind of thing used to take years,” said one.

But some arms control advocates argue that the Administration has not done enough.

“This isn’t going to happen, if the current Administration doesn’t push it--and we haven’t seen any sign that they’re inclined to push,” said Jack Mendelsohn, deputy director of the private Arms Control Assn. “Unless someone in the Administration is prepared to shake the bureaucracy, it isn’t going to happen. I hope it does happen, but I don’t think it will.”