Bush Asks Yeltsin Aid to Finish Nuclear Pact : Diplomacy: President is making effort to complete treaty on strategic weapons before term ends.

President Bush has launched a last-ditch effort to complete the unfinished U.S.-Russian strategic arms reduction pact before the end of his Administration, and he telephoned Russian President Boris N. Yeltsin this week to press the issue personally, officials said Thursday.

Yeltsin responded warmly that he also wants to sign a finished treaty before Bush leaves office, the officials said.

“Yeltsin said, ‘I’d like to sign it,’ ” a senior official said. “He wants to do this as an accomplishment with George Bush. He’s a sentimental man who feels a very strong tie with the President.”

In several letters sent to Moscow this week, Bush has pressed Yeltsin to drop several demands that Russian negotiators have made for changes in the framework agreement the two presidents made informally in June, officials said.

Administration officials suspect that Russian negotiators from the ministries of foreign affairs and defense have been demanding concessions that Yeltsin himself does not feel strongly about--and that the Russian president may overrule his diplomats in response to Bush’s personal appeal.

Yeltsin has indicated that he may reply to Bush by some time next week, the official said.

The agreement, commonly called START II, would cut 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 would commit both nuclear powers to eliminate missiles that carry multiple warheads, the most dangerous nuclear weapons.

After the two presidents announced their basic agreement in June, however, Russian military leaders complained that the deal required more cuts from Russia than from the United States.

Senior Bush Administration officials said that the United States does not intend to accept any major changes--partly because the changes would require U.S. concessions in important issues but also because they do not want to accept the idea that the Russians can renegotiate a pact that their president agreed to six months ago.

Officials said they also have warned the Russians that if they fail to reach agreement by Inauguration Day, the incoming Administration of President-elect Bill Clinton may need several months of preparation before it can get back to the negotiations.

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

* Downloading--The agreement requires both countries to destroy all multiple-warhead missiles, but the Russians want to change some multiple-warhead SS-19 missiles into single-warhead missiles by removing all but one warhead--an arrangement that would save them billions of rubles. U.S. officials have objected that this arrangement, known as “downloading,” would be difficult to verify.

* Silos--The Russians have agreed to destroy all their giant SS-18 missiles, but they want to use the hardened underground silos that housed the SS-18s for other missiles. The two countries appear to be working toward a compromise.

* 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 II. The Russians want more reassurance that the non-nuclear bombers cannot be converted quickly into nuclear bombers. But the Air Force objects to any such limits.

* 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 (“Star Wars”) has been trying to develop. The Bush Administration has agreed to this request.