President Boris Yeltsin, who has slipped out of public view as Russian troops have advanced into Chechnya, may take an unexpected vacation this month because of strain and "other factors," his spokesman said today.

Press secretary Dmitri Yakushkin did not specify what the other factors were nor a precise time for the holiday. The announcement immediately stirred speculation here that Yeltsin, who has a history of heart trouble, may be preparing for another operation.

Yakushkin said, "of course this strain calls for some breather, undoubtedly, it is very hard to work in such a rhythm, taking into account his age and other factors."

Yeltsin, 67, underwent coronary artery bypass surgery in late 1996 after a series of heart attacks, some of which were kept from the public during his reelection campaign. Informed sources have said in recent months that Yeltsin continued to suffer periods of inattention that may be caused by circulatory problems.

However, the Kremlin has not acknowledged that Yeltsin is suffering such difficulties. Recently, the Russian president said he felt better after a procedure to relieve pain in his back.

In Waco, Tex., Michael E. DeBakey, the American heart surgeon who advised the medical team that treated Yeltsin three years ago, said today he had heard nothing about new heart problems.

"I have to assume that he has not had any medical problem, because they usually call me if there is," DeBakey said. "They would certainly call me if there was any major problem with his heart condition."

DeBakey said he spoke yesterday with Renat Akchurin Yeltsin's surgeon, on a different matter. No mention was made of the Russian president's health.

"I get all kinds of rumors about him," DeBakey said. "I don't know where these start, but I can tell you that the great majority of them have no basis in fact."

Staff writer David Brown in Washington contributed to this report.