MOSCOW, FEB. 7 -- Moving away from seven decades of totalitarian rule, Soviet Communist Party leaders voted today to give up the party's constitutionally guaranteed monopoly on power and called for creation of a presidential system of government.

Addressing a press conference at the end of a stormy three-day meeting of the Communist Party's policy-making Central Committee, senior aides to Soviet leader Mikhail Gorbachev hailed today's decisions as a turning point for the Soviet Union. But they also suggested that the transition to Western-style multi-party democracy will be slow and complicated, with legal restrictions on formation of political parties.

Since Gorbachev came to power five years ago, the Soviet political system has steadily been liberalized to allow participation of informal groups and movements that have won mass support across the country. Even so, today's declaration by the Central Committee marked a stunning ideological reversal for a party that once claimed to be the sole force capable of representing the working class and building the world's first socialist state.

"We have taken a step of exceptional magnitude," said Alexander Yakovlev, a strong Gorbachev ally in the party's ruling Politburo and a key member of the team that drafted the new party program. "This shows that our party is undergoing changes of historic proportions. Power is being transferred from the party to the soviets," the Russian word for directly elected governing bodies.

Yakovlev said that the Communist Party leadership would propose changes in Article 6 of the Soviet Constitution, which describes the party as the "leading and guiding force of Soviet society and the nucleus of its political system." The amendments will be considered at the next meeting of the Congress of People's Deputies, the country's ultimate legislative authority, which is due to convene in May or June.

Today's vote followed a tumultuous year in Eastern Europe, as long-ruling Communist parties throughout the region have been forced to give up their constitutional guarantees of power.

"We do not exclude the possibility of the creation of any socio-political movement that shares the goal of the renewal of socialism," Yakovlev said, using a formula that appears to exclude legalization of overtly non-Socialist parties. He refused to be more specific about which parties would be allowed to operate, saying this would be a question for the congress to decide.

Participants in the Central Committee meeting, held in the Kremlin, said that the only member to vote against the draft program was former Moscow party chief Boris Yeltsin, a leader of the party's populist wing. Yeltsin, who has called for an immediate transition to multi-party democracy and a free-market economy, contended that the plan was not radical enough.

The vote in favor of the program represented a significant political victory for Gorbachev after weeks of mounting criticism from left and right. The 59-year-old Kremlin chief has spent most of the past two weeks closeted with a handful of close aides, rewriting the program to make it acceptable to the 249-member Central Committee, a body dominated by conservative apparatchiks.

In a move that could further strengthen Gorbachev's political position and enhance his personal power apart from the party, the Central Committee called for the congress to create a new, powerful presidency that would be filled by direct popular election. At present Gorbachev is head of state by virtue of his position as chairman of the Supreme Soviet, or standing legislature, and theoretically could be forced from that post in the event of a Communist Party revolt against him.

"The president should be responsible to the people and elected by the people," Politburo member Anatoly Lukyanov, Gorbachev's deputy on the Supreme Soviet, told reporters. Lukyanov said that the new presidential post would draw on Soviet and Western experience, but refused to offer details about the likely extent of presidential authority.

In addition to chairman of the Supreme Soviet and general secretary of the Soviet Communist Party, Gorbachev is commander-in-chief of the armed forces, a post he holds as chairman of the state Defense Council. But his supporters insist he should be given more power to steer the Soviet Union through the current critical period. With today's vote, the focus of power appeared to have shifted further toward Gorbachev.

Secretary of State James A. Baker III, who arrived here today for talks with Soviet leaders on preparations for a Gorbachev-Bush summit in late June, said in a statement that the United States supports Soviet moves toward political pluralism. Baker held three hours of talks here this evening with Foreign Minister Eduard Shevardnadze.

Although rival political organizations have emerged in the past few years, they lack the organizational structure of the Communist Party, which is represented in every factory, military unit and state institution. The new groups have largely operated at the margins of Soviet politics.

An exception has emerged in the three Soviet Baltic republics, where the Social Democrats have become a major political force in the last few months, as rank-and-file Communists deserted the ruling party in droves. One Soviet academic, Boris Orlov, has predicted that the Baltic Social Democrats will win 30 percent of the votes in the republics' elections this month and next.

Yakovlev said that the issue of registering new political parties would be included in a draft law on social and public organizations being considered by the Supreme Soviet. "As for what parties can be established, it's difficult to guess," he said. "It's necessary to go through the legislative process, the process of registration and so on. Perhaps the Supreme Soviet will decide what parties can exist. This is not for our party to decide."

While formally renouncing the party's monopoly on power, the Central Committee resolution appeared to reserve a special place for the Communist Party in the Soviet political system. It stated that the Communist Party "and other social and political organizations and movements" would participate jointly in running the country and nominating candidates for soviets -- the local governing councils.

Except for a few months after the November 1917 Bolshevik Revolution, the Communist Party has been the Soviet Union's only legal political party. A rival left-wing party, the Socialist Revolutionaries, left the government in March 1918 and was disbanded six months later during what later became known as the period of "Red Terror."

During the last relatively free elections in the Soviet Union just after the revolution, the Socialist Revolutionaries won 40 percent of the vote for a consituent assembly, compared to 24 percent for Bolsheviks, or Communists, and 4.7 percent for the right-wing Cadets. The assembly was disbanded shortly after its inaugural session in January 1918.

This week's three-day Central Committee meeting was marked by angry exchanges between progressives and conservatives, with some speakers accusing Gorbachev of leading the country to the brink of disaster. But while Central Committee members differed sharply on attributing blame for the crisis, there was a broad consensus that the Communist Party was obliged to reform itself radically if it wants to remain the dominant political force in Soviet society.

Claims by hard-liners that the Soviet Union was nearing catastrophe were rejected by Yakovlev and other Gorbachev supporters on the ruling Politburo. Yakovlev told the session that a crisis would certainly erupt "if we act belatedly, limit ourselves to wishy-washy decisions, if we waver or flinch."

Other members of the 12-man Politburo -- including Shevardnadze, ideologist Vadim Medvedev, and KGB chief Vladimir Kryuchkov -- all supported Gorbachev's proposed reforms of the party. They also expressed support for the idea of a strengthened presidency at a time when the Soviet Union is facing mounting economic turmoil and ethnic unrest.

Speeches at the session suggested that the process toward multi-party democracy is likely to be slow and tortuous and will probably be combined with attempts to increase the authority of the state. Kryuchkov, who is regarded as a key Gorbachev ally, called for a new law banning extremist organizations and "those calling for extremist acts."

Describing the current political situation in the country, the KGB chief denounced "destructive, anti-Socialist aims" of opposition political forces. He said the political spectrum ranged from the radical left to supporters of "openly nationalistic, anti-Communist and even monarchist ideas."

Gorbachev's supporters rejected assertions by conservatives that the Kremlin was to blame for the ouster of Communist regimes in Eastern Europe. The Soviet news agency Tass quoted Shevardnadze as telling the comittee that the hard-line Communist governments of Eastern Europe had been destroyed "by the will of peoples who no longer wished to tolerate coercion."