When the last war in Chechnya began nearly five years ago, President Boris Yeltsin slipped out of public view as Russian generals plunged disastrously into a ground war in the rebellious southern region.

For two weeks, Yeltsin was hospitalized for what aides described as a routine nose operation. Now, as an estimated 50,000 Russian troops have advanced cautiously into northern Chechnya, Yeltsin has again all but disappeared.

Leaving the matter entirely in the hands of his generals and Prime Minister Vladimir Putin, Yeltsin failed to show up this week for a meeting of the Kremlin security council, which he chairs and which approved a revised national security document calling for increased defense spending.

His absence is just one of the echoes of 1994 that has raised questions here about whether Russia has learned the bitter lessons of the last conflict, which left tens of thousands of civilians dead. Yeltsin has called the two-year Chechen war his gravest mistake.

Yeltsin has been in and out of view for years as he struggled with ill health and sought to keep his distance from painful and unpopular developments here. He has been sidelined, often for months at a time, with a heart condition, and sources say he still suffers from circulatory problems, although he claimed recently to be feeling well.

His low profile also may be driven by a desire to avoid difficult situations and let cabinet ministers take the heat. He has fired five prime ministers in the past 18 months, often waiting in the wings and then acting abruptly. There are also big political stakes -- fallout from another military failure in Chechnya could reverberate into next year's election to choose Yeltsin's successor.

Analysts and politicians here say the latest advance into Chechnya -- to create a "security zone" across the region and bar Chechen guerrillas from promoting rebellion in adjacent Russian territories -- carries the risk of a drawn-out battle against seasoned Chechen defense forces. And, they said, Moscow will find it more difficult to arrange a negotiated settlement than in the last war because Chechnya is more fragmented and weaker than it was three years ago.

"We have a Catch-22," said Vladimir Averchev, a member of the centrist Yabloko faction in the lower house of parliament, the State Duma. "While in principle everyone agrees we should do everything to find a political solution, it's unclear how to do it, and with whom."

On paper, Yeltsin sits atop what Lilia Shevtsova, a senior associate at the Carnegie Endowment for International Peace here, has described as a "super-presidential regime," in which he has exercised power as the hands-on arbiter between key interest groups. But Shevtsova noted in a recent book on Yeltsin that the political structure is breaking down because of Yeltsin's ill health and because others no longer respect his decisions. The leader of the upper house of parliament said recently that Yeltsin controls nothing in Russia beyond the Kremlin walls.

Yuri Korgunyuk, an analyst with the Indem Center for Applied Political Studies, a research organization here, said that Russia is using a carrot and stick approach with Chechnya, what Russians call the whip and gingerbread. "It is more or less understood what is meant as a whip," he said of the military's measured advance into Chechnya. "It is so far completely unclear what is meant as gingerbread. There is no concrete plan here. They are not raising the question -- `All right, we will seize, occupy Chechnya. And what is next?' How is this problem going to be resolved next?"

The latest fighting broke out in August after Chechen guerrillas crossed into the neighboring Russian region of Dagestan, seized several towns and declared their intention to establish an Islamic state there. Russian troops repelled the guerrillas but a string of deadly bomb attacks on Russian apartment buildings that the Kremlin blamed on Chechen militants led Moscow to order airstrikes on key Chechen installations and to deploy troops at the border. Thousands of civilians have fled the fighting, and Russian troops now occupy the northern third of Chechnya.

In some ways, the mistakes of the last war still reverberate here. Putin suggested installing a pro-Russian puppet government in the region, a comment redolent of the reliance Moscow placed on unpopular surrogates in the earlier conflict. Military leaders also have spoken of a quick "surgical" strike and a quick victory, much as they miscalculated before.

But in other ways, this Chechen conflict is different from the last. Averchev recalled that the earlier war was seen by the Chechens as a brutal attempt by Moscow to impose its will and crush independence sentiment there. This time, he said, Russia is on the defensive, reeling from the attacks in Dagestan and the apartment house bombings, in which nearly 300 people died. He said Russian public opinion has "changed very seriously" in part because of what happened in Chechnya after the first war, when the region sank into a state of lawlessness in which kidnapping and the slave trade have thrived.

In field tactics, too, the Russian advance has been different from that of 1994, when army commanders threw into battle ill-trained conscripts who were unprepared for the terrain, the foul weather and the ferocity of their foes. This time the army has advanced cautiously.

Averchev said the military now realizes that public "support for this operation is conditional" on mitigating losses among Russian troops. Korgunyuk said that the military learned a lesson from the public resentment over the last war "that is necessary to at least prevent the rise of anti-military moods inside Russia itself and to try to bypass the issue of human losses among the soldiers, including new recruits." He said the army had accomplished this so far by "strict military censorship and by cutting off other sources of information about the military operation."

Politicians and analysts also worry that Moscow has no strategy for a negotiated settlement of the conflict. Chechen President Aslan Maskhadov has been severely weakened by internal opposition, while the leader of the Dagestan incursion, guerrilla commander Shamil Basayev, has vowed more attacks on Russian territory.

Yeltsin is also politically weaker than ever, and his disappearance from view may signal his uncertainty, Korgunyuk said. "Yeltsin indeed has this trick," he said. "When he does not know how to solve a problem and hesitates between this or another variant, it is sometimes impossible to drag him out with pincers. He keeps silent for a long time."