MOSCOW, NOV. 7 -- Soviet leader Mikhail Gorbachev made a three-way bid this week to boost the sagging stock of Communist and left-of-center parties across Europe, offering support to the beleaguered and out-of-power in U.S.-allied countries of Western Europe and the promise of greater leniency toward the Soviet-allied regimes in the East.

Despite Gorbachev's overtures, however, a week-long parley of international Communists and left-wing movements at the Soviet Union's 70th anniversary celebrations here has produced few tangible results.

While participants from both Eastern and Western Europe praised the Soviet leader's reforms, most stressed that they have so far failed to stem the downhill slide of Eurocommunism in Western Europe or even to gain full support in the Communist-ruled countries of the Soviet Bloc.

In a signal that Moscow would encourage greater freedom in Czechoslovakia, Hungary, Poland and the other countries in the Soviet Bloc, for example, Gorbachev used a speech Wednesday to reject the "arrogance of omniscience. It speaks of a tenacious habit to reject other points of view out of hand," he said.

"We do not in the least claim a monopoly on the truth," Gorbachev said. "We are engaged in search ourselves and invite others to look jointly."

Another Soviet official buttressed the call for more independence in Eastern Europe by suggesting that the Soviet Union review the events surrounding the "Prague Spring." Since the 1968 Soviet invasion and crackdown against the Czechoslovak experiment in democratic socialism is considered one of the biggest psychological barriers to initiative in Eastern Europe, some Soviet Bloc diplomats in Moscow reacted favorably to the suggestion.

But the signals to Eastern Europe are mixed. Czechoslovakia's conservative regime, which has been reluctant to embrace Gorbachev's call for reforms, appears cautious about a review of the Prague Spring. Czechoslovak leader Gustav Husak, 74, who helped dismantle the reforms that brought about the Prague Spring, had been in Moscow for the 70th anniversary. But he left one day after discussion of the issue began here.

In a speech in Prague on Friday, Husak said that the Prague Spring had begun to threaten socialism. "We had to pay dearly for the retreat from these principles," CTK, the official Czechoslovak news agency, quoted him as saying.

Still, Gorbachev's reforms have given a bigger impulse to the Communist-ruled countries of Eastern Europe than to the Communist parties of Western Europe, according to participants in discussions here this week.

French Communist leader George Marchais pledged support for Gorbachev's policies of disarmament and perestroika, or reconstruction, in a speech on Wednesday.

Italian Communist Party leader Alessandro Natta also praised Gorbachev's policies and emphasized the attempts of Italian Communists to work with other leftist forces in a common fight.

Despite the increasing popularity of Gorbachev over the past 2 1/2 years, however, both Natta's and Marchais' parties have lost support at home. Since 1982, for instance, electoral support for the French Communist Party has declined from 18 percent to below 10 percent. Italian Communists also have suffered losses.

One of the main reasons that Gorbachev's popularity has not spread to the Communist movements of Western Europe is that his policies of economic reform and glasnost, or openness, are not applicable to the West, diplomats here said.

The diplomats also said that Gorbachev's own stress on cooperating closely with ruling parties in the West undercuts the importance of the role played by minority Communist parties.

In an apparent attempt to stake out the common ground between Eastern and Western Europe, Gorbachev invited such noncommunist left-of-center parties as Italy's and France's Social Democrats and West Germany's Greens to participate in Soviet anniversary celebrations for the first time.

Part of the reason, the Soviet leader acknowledged, was to buttress declining Soviet influence in the West. "We ourselves felt strongly how socialism's international impulse was declining in the stagnation period," he said Wednesday, "so perestroika in the Soviet Union became vital from this end as well."

"What is needed," he added, "is a more sophisticated culture of mutual relations among progressive forces, the kind that would make it possible to accumulate all the diversity of experience and that would appreciate the varicolored diversity of the surrounding world."

"There must be joint action," Gorbachev said, "but of course in up-to-date forms."

Noncommunist participants reacted reluctantly to the call. Most agreed to come to Moscow on the condition that no joint statement or communique be issued that would put them squarely behind Soviet leadership. "We came because we were curious," a visitor from France's Socialist Party said in an interview, "not because we are in favor."

One member of Italy's Socialist Party, breaking ranks with the widespread praise bestowed on Gorbachev's keynote speech at the conference, accused the Soviet leader of a lack of respect for the contribution of European socialism.

"Can we agree with assertions that socialism takes its beginnings in Russia of 1917?" Italian legislator Laura Fincato asked in a speech Thursday, published in the Soviet newspaper Pravda. "And that only here, and only since that time, it secured the main achievements and secured fundamental results?"

"Putting the question this way," she added, "leads to the underestimation and disregard of experience accumulated in Europe and other parts of the world."