President Clinton turned to Russia's Boris Yeltsin this week to seal a shaky deal with Serbia on a cease-fire in Kosovo. This is not a cost-free transaction for the United States. Yeltsin's bill is already in the mail and is likely to run high.

Russia's political future is in play as the Kosovo settlement takes final shape. The signals from Moscow are unambiguous: The severely ailing Yeltsin is trading unpopular intervention on Kosovo to maintain U.S. support for his embattled regime now and in the future for the successor Yeltsin has finally selected: Sergei V. Stepashin.

Clinton and Deputy Secretary of State Strobe Talbott, the president's chief adviser on Russia and Serbia, have made a down payment to Yeltsin by extravagantly praising the role Russia has played in the Kosovo negotiations thus far. In fact the Russian contribution to cornering Slobodan Milosevic has been largely grudging and mixed in its effectiveness.

Payment in the form of background briefings is rhetoric easily spent by Clinton, who has made a career of dodging bullets but now seems to be dodging a radioactive comet that was hurtling at him a week ago.

Clinton was still avoiding making an immediate decision on ground troops when word reached him at a Cabinet meeting on June 3 that Milosevic had unexpectedly accepted the terms taken to Belgrade by Russian envoy Viktor Chernomyrdin and Finnish President Martii Ahtasaari. As a look of happy relief spread across his face, Clinton told his Cabinet: "Don't gloat."

That was prudent advice. The settlement was immediately called into doubt by Milosevic's efforts to create new loopholes in cease-fire terms Talbott had virtually dictated to Chernomyrdin and Ahtasaari in talks in Bonn. Foreign ministers of the Group of Seven had to renegotiate with Russia and fill in blanks that remained in the Talbott terms at a contentious two-day meeting in Cologne, Germany, this week.

Russian Foreign Minister Igor Ivanov was no more constructive in that meeting than he had been in the Bonn talks, where he intervened several times to keep a frequently wavering Chernomyrdin from going wobbly on Milosevic. In Cologne, Ivanov informed the G-7 diplomats that the terms they sought exceeded his instructions and he could not agree to anything.

That triggered two phone calls by Clinton to Yeltsin, who once again pulled back Ivanov -- after the foreign minister secured some word and timing changes that give the Serbs new wiggle room.

Moscow observers are unsure why Ivanov, originally appointed by ousted Prime Minister Yevgeny Primakov, has taken such a hard line. Ivanov may hope to preserve his political viability for future governments by flowing with the rising tide of criticism in Moscow of the deal and the Russian role in it. Or he may hope to protect the foreign ministry against retaliation from the Milosevic-friendly Duma.

Russian resistance has been glossed over by Clinton, Talbott and other U.S. officials who highlight Stepashin's friendliness. A major clue to his importance and to Yeltsin's newly flagging health came on May 31, when Yeltsin placed a call to Clinton and then was "unavailable" when the president called back. Instead it was Stepashin who conducted the 30-minute call with Clinton, who before has let Vice President Gore deal with Yeltsin's revolving-door prime ministers.

The Russian president preemptorily installed Stepashin as his prime minister last month in the fourth abrupt change of Russia's government in the past 18 months. He fired the faithful Chernomyrdin in March 1998 without warning and repeated this pattern with Sergei Kiriyenko and Yevgeny Primakov when they seemed unable or unwilling to protect Yeltsin, his family or close associates against corruption investigations.

Stepashin is an ultimate Yeltsin loyalist whose background is in internal security. He has surprised Moscow analysts by getting control over the unwieldy, heterogenous cabinet Yeltsin picked for him. But he is seen at home primarily as Yeltsin's protector and enforcer, not a statesman.

Momentarily building up Stepashin and continuing to turn a blind eye to the instability that Yeltsin's smash-and-rule governing tactics foster in Moscow would seem to be cheap payment by the Clinton administration for help with a Kosovo settlement.

But Russia's fate is at stake in the internal drama leading toward presidential elections next year. Getting too deeply and visibly involved in Russian domestic politics in return for gains in Kosovo now could be a bad bargain with the future. Wariness, about Russian intentions on Kosovo and about Russian politics, is the wise attitude right now.