In its eagerness to get relations with Russia back on track, the Clinton administration is playing down what may be the biggest threat to the relationship's long-term health -- the possibility that Boris Yeltsin will trample on his constitution to keep himself in the Kremlin.

Russia is scheduled to hold parliamentary elections in December and to elect Yeltsin's successor next July, when his second -- and, legally, final -- term expires. That July 2000 vote should be a historic moment, the first time one Russian leader will be peacefully exchanged for another as an expression of the people's will.

But Moscow already is having a bad case of transition jitters. There's increasing speculation that Yeltsin will engineer a reunion between Russia and the former Soviet republic of Belarus. The newly born nation naturally would need a new constitution; that could give Yeltsin a constitutional fig leaf to extend his rule.

Yeltsin fed this rumor when, in a recent interview with the German magazine Der Spiegel, he hailed a possible union as "rooted in the community of the historic fates and the friendship between our peoples." Preposterously, given that Belarus is led by a Soviet-style strongman, Yeltsin also proclaimed that union is a step "taken of their own free will by the states and peoples."

The other conspiracy theory whipping through Moscow these days envisions Yeltsin banning the Communist Party. He fed this one, too, when he publicly chastised his justice minister for not reining in "extremists" such as the Communists.

Given that the Communists operate legally and with considerable popular support, a ban would constitute a devastating blow to democracy. But, the theory goes, it might weaken Yeltsin's opposition enough to allow him to install a reliable successor as president. Or -- to take the conspiracy theory one heated step forward -- a ban would elicit such a violent reaction that Yeltsin could call in his troops to restore order and then cancel next summer's presidential election in the name of stability.

Moscow is never free of such rumors, and most of the time they come to nothing. Some of Yeltsin's closest advisers urged him to cancel the 1996 presidential election at a time when he seemed sure to lose, but he chose to battle it out instead.

This time around, too, Yeltsin may have no doubts about letting democracy take its course. He may be talking up union with Belarus to co-opt a nationalist issue, with no intention to follow through. He may be rattling the Communists just to keep them off guard, to remind Russia that he remains a player despite his varied illnesses -- or simply because rattling Communists is one of his favorite sports.

Still, there are reasons to worry that Yeltsin or his entourage might be more tempted this time to commit foul play. The current frontrunner for the 2000 election is Moscow's mayor, Yuri Luzhkov, whose cheery smile fools no one into doubting that he would crush any opponent if doing so proved convenient.

In early 1996, Yeltsin seemed sure to lose to another implacable foe, but at least he had a candidate: himself. Today his camp's hope is the current occupant of the prime minister's chair, but to most Russian voters Sergei Stephashin isn't much more than that -- current occupant. Unlike Nelson Mandela, in other words, Yeltsin has no loyal successor and no loyal political party to ensure that his legacy will be respected.

And Yeltsin and his entourage have to worry about more than whether Russia builds statues of him as father of the nation. Already, Russia's procurator-general has been delving into reported corruption close to Yeltsin himself. Yeltsin keeps trying to fire this investigator, and the parliament keeps insisting that he remain. The day Yeltsin leaves office, this standoff will end. Bank accounts, dachas, even personal freedom -- nothing will be guaranteed.

The logical response to this dilemma is to begin establishing civilized rules of transition and to treat opposition figures with some respect. It should be obvious that the alternative -- trying to engineer a legal coup -- would be a disaster. Yeltsin's popularity rating hovers around 2 percent, with a margin of error that puts him into possible negative territory. The military would not likely rally to his defense. The West, including the Clinton administration, would not stick with him.

All this should be obvious, but it may not be. And that is where the administration has to enter the picture. Senior administration officials understand that almost no possible successor could be worse for Russia and for U.S.-Russia relations than a disruption in the democratic process -- not the nationalist Mayor Luzhkov, not the retired general Alexander Lebed, not the Communist Gennady Zyuganov.

But they are not communicating this to Moscow. On the contrary, when national security adviser Sandy Berger calls the most recent Clinton-Yeltsin meeting "one of the best" and describes Yeltsin -- who every Russian knows is bloated and ailing -- as "very much in charge" and "very forceful," he feeds the Russian perception that America values the Bill-Boris friendship above all. That's a misperception, and the administration needs to say so, very forcefully.

The writer is a member of the editorial page staff.