MOSCOW, JAN. 14 -- Finance Minister Valentin Pavlov, an advocate of a gradual shift of the Soviet economy to a market system, won legislative confirmation as the country's new prime minister today after his nomination by President Mikhail Gorbachev.

Pavlov, 57, an economist, will replace Nikolai Ryzhkov, who suffered a heart attack last month and who had been the target of criticism for more than a year because of his resistance to proposed radical changes in the centralized Soviet economy. Ryzhkov's replacement leaves Gorbachev as the only remaining member of the leadership team that took power in March 1985.

After perfunctory discussion, the legislature confirmed Pavlov by a vote of 279 to 75. In the newly restructured government, he will have far less power as prime minister than Ryzhkov because ultimate responsibility for the economy has shifted to the president.

The independent news agency Interfax reported that the Soviet ambassador to the United States, Alexander Bessmertnykh, will likely be proposed soon as foreign minister, replacing Eduard Shevardnadze. Shevardnadze resigned last month to protest what he called an approaching dictatorship. Interfax, which has been generally accurate in such reports in the past, cited Foreign Ministry officials in its dispatch.

The Soviet Embassy in Washington said Bessmertnykh, 57, left for Moscow Sunday after being summoned for "consultations," Washington Post staff writer Don Oberdorfer reported. U.S. officials in Washington said they had no information on the reason for Bessmertnykh's trip, but they noted that several other Soviet ambassadors reportedly had been called home as well.

Bessmertnykh's appointment would hold out hope to Soviet radical-reform advocates and Western governments that the Soviet Union will continue "new thinking" in foreign policy that began nearly six years ago and brought about an easing of East-West tensions. However, the international condemnation of Sunday's Soviet army attack in Vilnius, Lithuania, is certain to complicate the work of any new foreign minister.

If Bessmertnykh is nominated, it is likely he will face harsh criticism from hard-liners who feel that career diplomats in Shevardnadze's circle at the Foreign Ministry sold out Moscow in dealings with the West on arms control, German unification and troop withdrawals from Eastern Europe.

Some conservative legislators have indicated a preference for a figure such as Yevgeny Primakov who, as the Soviet Union's special envoy to the Middle East during the Persian Gulf crisis, clashed with Shevardnadze over policy.

While Gorbachev described Pavlov as an "outstanding economist and financial expert," radical-reformist members of both the Soviet and Russian legislatures expressed concern that Pavlov's approach to reform was no more aggressive than Ryzhkov's. Last year, Ryzhkov beat back attempts by Gorbachev's more radical economic advisers to institute a program for transfer to a market economy in 500 days.

"The transition to a market economy must be pursued consistently," Pavlov told the lawmakers. "But it must be done in a way so that the poor suffer least of all from the difficulties of the social changes that we will have to go through."

Gorbachev arrived at the legislature to nominate the new prime minister at midday, just after members finished an emotional debate on the Lithuanian crisis, but he did not mention the crisis during his presentation of Pavlov.