The Kremlin's savage war against Chechen rebels brings Russia's presidency within the grasp of a hard man who shows no pity toward those in his way. But hard can become brittle in a blink of history's eye. And Vladimir Putin still has to demonstrate which he is when things go wrong.

Putin became Russia's acting president with Boris Yeltsin's New Year's Eve resignation. The transfer of power was a deftly managed political lock-in operation:

Putin took power while his commanders were still moving forward in Chechnya, while his allies were counting their gains in December's Duma elections and while Putin was riding high above all rivals in opinion polls. He dominates the field for the election that he must organize within 90 days.

The gains were equally clear for Yeltsin. He at last had a successor popular enough to uphold the immunity deal he had to have before he would leave office. Putin's ruthless prosecution of the Chechen campaign gives him a shot at enforcing his first official decree, which promised Yeltsin protection in retirement.

It was past time for Yeltsin to step down. He has been ineffective as a national leader since multiple heart attacks in 1996. But ego and a succession of politically weak or unreliable prime ministers who would have been unable to protect him kept him in the Kremlin.

This was a deal worth shaving six months off the ailing Yeltsin's second term--for the two men. But Russia and the world still know too little about Vladimir Putin to be confident about what will come next.

The smoothness of the transfer of power has generated expectations of stability to come for Russia. That is clearly the hope of the Clinton administration, which was surprised by Yeltsin's decision but not distressed to see him finally go.

The presumption of redeemability that the administration offered Yeltsin throughout his erratic tenure wore thin in his final months. Now the Clinton team must resist what will be its natural temptation: to extend that presumption to Putin immediately and get involved once again in the Russian elections on the side of "reformers"--a phrase Secretary of State Madeleine Albright seems to use as synonymous for people who do or will do favors for the United States.

A Yeltsin-tendered invitation for Clinton to visit Moscow in the spring is on the table. Putin's intention to reduce the war in Chechnya by then to a heavy but static occupation through a cosmetic political settlement dictated to local puppets is apparent. So is his hope to get the Duma to move on the stalled START II treaty ratification.

But these are not sufficient to justify high-profile U.S. involvement on his behalf. The administration should not warmly embrace the new Kremlin boss and claim vindication of its Russian policy on the strength of those moves alone, which show Putin's KGB-honed skill of manipulation and sense of timing as much as anything else.

Putin must conduct elections that demonstrate a genuine commitment to democracy and stability for Russia. And he must include Chechnya's elected president, Aslan Maskhadov, in serious negotiations to end the war. Washington can play the crucial role in turning Putin away from a cosmetic but unstable settlement to the war by making clear now that it will not embrace such an outcome.

Would Putin be sensitive to outside opinion? There are reasons to think so. It matters that Putin, who is 47, is a rarity among Kremlin leaders: He has lived outside his national frontiers and is proficient in a foreign language. He learned German when he was posted by the KGB to East Germany in the final Soviet years, at a time and place when many of its agents were involved in setting up or managing commercial enterprises for the agency.

His contacts with politicians from his native St. Petersburg, especially Yeltsin favorite Anatoly Chubais, were instrumental to his making his way into the presidential administration and into Yeltsin's favor after the KGB.

Yeltsin leaves behind a Russia mired in a bloody war, a failed economy and galloping corruption that will undermine Putin's rule if he does not deal with it quickly. Yeltsin never dealt with it at all. He strides into history resembling the fictional financier of whom Anthony Trollope wrote:

"Such a man rises above honesty as a great general rises above humanity when he sacrifices an army to conquer a nation. Such greatness is incompatible with small scruples. A pygmy man is stopped by a little ditch, but a giant stalks over rivers."