U.S. SPECIALIST ARRIVES TO CHECK YELTSIN.

Byline: Dave Carpenter Associated Press 

Amid rising fears that Boris N. Yeltsin's health is too fragile right now to withstand heart surgery, a top American cardiovascular surgeon flew in Monday to offer his opinion. Meanwhile, the Communists demanded that Yeltsin step down if he can't govern.

Russian stocks slid 3 percent on concerns over Yeltsin's health, and the credibility of official reports on his condition crumbled. Terse official accounts of a basically healthy patient heading into routine surgery have fallen apart, challenged by Yeltsin's doctors themselves.

Television newscasts led with the arrival of heart specialist Dr. Michael DeBakey, who will join in examinations Wednesday that could set a date for Yeltsin's bypass operation.

The top Russian surgeons who invited DeBakey are now talking about delaying the operation because of related health concerns.

While declaring ``I'm always optimistic,'' DeBakey told reporters he could give no specifics because he had not seen Yeltsin yet.

Dr. Renat Akchurin, the president's surgeon, said over the weekend that the operation may have to be delayed for up to two months while Yeltsin's health is stabilized. The president, who has been in the Kremlin hospital since Sept. 13, said earlier that the operation would be late this month and reportedly is pressing doctors to operate.

``The operation most probably won't take place this month, but the final decision will be made by doctors at Wednesday's consultation,'' Yeltsin press spokesman Sergei Yastrzhembsky told the Associated Press.

Akchurin, in a Russian television interview Sunday, said proceeding with the operation at an early date ``might entail some risk.''

Without being specific, he suggested that Yeltsin may have been overdoing things recently, such as fishing and hunting, which are ``not recommended.''

Despite the widespread concern that Yeltsin is seriously ill and no longer running the government, the president has been seen on television meeting with aides regularly and appears to be in overall control.

But talk about a delay and more serious problems has intensified the political ruckus over both his health and his reluctance to step aside for all but the briefest time.

The Communist speaker of parliament, Gennady Seleznyov, said Monday that Yeltsin should resign if doctors tell him to do less work instead of having a heart operation.

``He should himself ask to leave'' his post if this happens, the state Duma speaker said. ``Russia doesn't have the kind of situation that allows (the president) to reduce his work intensity.''