Russian acting president Vladimir Putin promises to clean up widespread corruption. After this background report, Gwen Ifill leads a discussion of with experts.

GWEN IFILL: Russia greeted the new year with a new leader. He is Vladimir Putin, a former KGB agent who was virtually unknown at home and abroad until four months ago, when Boris Yeltsin plucked him out of obscurity to become prime minister. After Yeltsin's surprise resignation Friday, Putin became acting president. Already leading in the polls as a candidate for the job, he now has the advantage of incumbency. He is heavily favored to win a full four-year term when elections are held in March. Russians have embraced Putin's tough handling of the war in Chechnya. Building on that popularity, Putin immediately traveled to Chechnya this weekend to visit Russian troops fighting there.

VLADIMIR PUTIN: (speaking through interpreter) Happy New Year to all of you, and all the best to you and your families. It took a lot for us to get here. We were meant to be flying here, but had to turn back. We finally made it by car. I have to apologize for the delay, but better to be late than never.

GWEN IFILL: That military campaign began after bombings in Moscow were blamed on Chechen separatists. Russian troops are now engaged in fierce fighting, closing in on the capital city of Grozny. Putin convened Russia's security council within hours of Yeltsin's resignation.

VLADIMIR PUTIN: (speaking through interpreter) In the government and foreign ministry, the principles of everything that has been decided by the president recently, by the first president of Russia, will be fulfilled.

GWEN IFILL: Putin remains an unknown quantity abroad. U.S. officials have not hesitated to criticize the Chechen war.

MADELEINE ALBRIGHT, U.S. Secretary of State: He's riding a tiger in this. I think there's no question. I mean, he has based a great deal of his style on what is happening in Chechnya and the fact that he went there. But I think we believe that there's a very dangerous aspect to this, in terms of quagmire, and that he needs to develop some kind of exit strategy.

GWEN IFILL: At 47 years old, Putin is now perceived as energetic and healthy in all the ways the 68- year-old Yeltsin was not. In his surprise resignation speech on Russian TV Friday, Yeltsin said he had been "naive" for believing Russia could transform itself overnight.

GWEN IFILL: But as part of his succession deal with Putin, Yeltsin will be immune from prosecution. Allegations of corruption have been directed at his top aides and family. Yeltsin's resignation came eight years after his former mentor Mikhail Gorbachev resigned, following the breakup of the Soviet Union. The rivalry between the two men dates back to the late 1980's, as Yeltsin, then a member of the Soviet parliament, made clear in a 1989 interview on the NewsHour.

JIM LEHRER: In this country, Gorbachev is seen by many in heroic terms as a man of history, a man who is turning around a huge ship of state in a very dramatic way. Is that the way we should see him? How should Americans view Mikhail Gorbachev?

BORIS YELTSIN: (speaking through interpreter) You have some euphoria of the first two years of perestroika. You don't know the real state of affairs in the country. If you knew it, you would not be so euphoric now.

JIM LEHRER: What should we be? If not euphoric, what?

BORIS YELTSIN: (speaking through interpreter) More realistic, more realistic.

GWEN IFILL: By 1991, Yeltsin had fully grabbed the world spotlight, climbing atop a tank outside government house in Moscow to denounce an attempted coup against Gorbachev by hard-liners and the KGB. Four months later, the hammer and sickle was lowered at the Kremlin. The Soviet Union was dissolved, replaced by a collection of republics independent of Moscow. (Crowd chanting "Yeltsin, Yeltsin") Even as leader of a diminished Russia, Yeltsin was initially a popular president. But his popularity plummeted as Yeltsin's market reforms led to skyrocketing inflation and unemployment. But Yeltsin staged a remarkable political comeback, winning reelection in 1996, even after suffering two heart attacks. But his health faded again, and he underwent multiple bypass surgery. Relations with the United States grew frosty, weakened, among other things, by the NATO bombing campaign in Kosovo. But President Clinton had only kind words for Yeltsin after news of his sudden resignation.

PRESIDENT CLINTON: Well, I liked him because he was always very forthright with me. He always did exactly what he said he would do. And he was willing to take chances to try to improve our relationship, to try to improve democracy in Russia.

GWEN IFILL: But in recent months, Yeltsin supported the Chechnya war, to the dismay of his colleagues in the West.