Prime Minister Nikolai I. Ryzhkov, who suffered a heart attack two days ago, was in serious condition Thursday but his health was not deteriorating, Mikhail S. Gorbachev told the Congress of People's Deputies.

"We have called in the very best specialists. They are working around the clock," the president said.Earlier in the day, Radio Moscow quoted Gorbachev's spokesman, Vitaly Ignatenko, as saying Ryzhkov's condition had worsened and "gives rise to grave concern."

But Gorbachev, who personally announced Ryzhkov's illness on Wednesday, described his friend's condition in more optimistic terms.

"His condition is serious but is not worsening. Everything possible is being done," he told the Congress, the country's highest legislative body.

Ryzhkov, 61, suffered a heart attack Tuesday night after lawmakers voted to eliminated the Council of Ministers he heads.