MOSCOW, NOV. 2 -- Soviet leader Mikhail Gorbachev, in a major speech delivered today on the eve of the 70th anniversary of the Russian Revolution, accused Joseph Stalin of "enormous and unforgivable" crimes, but stopped short of a full-scale denunciation of the dictator whose policies and purges are widely believed to have caused the deaths of millions of Soviets.

In the nearly three-hour speech, Gorbachev also criticized those who are trying either to block his reforms out of fear or to implement them too quickly out of impatience. He pledged to work "unremittingly" for a "palpable breakthrough" in strategic and space-based nuclear arms negotiations with the United States.

Gorbachev acknowledged that perestroika, or his campaign of economic and political restructuring, had put "growing pressure" on society. He referred both to "the resistance of the conservative forces that see perestroika simply as a threat to their selfish interests and objectives" and to those who "succumb to the pressure of the overly zealous and impatient."

"It should be clear that one cannot leap over essential stages and try to accomplish everything at one go," he said, in apparent reference to the recent high-level dispute over Boris Yeltsin, the Moscow party chief who reportedly criticized the party leadership for moving too slowly to implement some of Gorbachev's programs.

Gorbachev called the treaty with the United States on medium- and shorter-range weapons to be signed at a December summit with President Reagan in Washington "the first tangible step along the path of scrapping nuclear arsenals."

Of his upcoming talks with Reagan, Gorbachev said, "The world expects the third and fourth Soviet-U.S. summits to produce more than merely an official acknowledgment of the decision agreed upon a year ago, and more than merely continuation of the discussion.

"That is why we will work unremittingly at these meetings for a palpable breakthrough, for concrete results in reducing strategic offensive armaments and barring weapons from outer space -- the key to removing the nuclear threat." Gorbachev's mention of a fourth summit was a reference to an expected trip to Moscow by Reagan next year.

Today's speech had been billed in advance by Soviet officials as a major statement befitting the occasion of the 70th anniversary, which is dominating the Soviet news media and has drawn Communist Party delegations here from around the world. Almost one half of the speech was devoted to a review of history, which in Soviet terms is considered of key importance in setting current policy.

The Soviet leader, who spoke for 2 hours and 41 minutes, cast new light on once forbidden areas of Soviet history and sanctioned a public debate over the role of Stalin and other Communist Party leaders.

But he carefully balanced his revision of the party's official line on history, giving both liberals and conservatives equal due. Thus, Gorbachev for the first time publicly implicated Stalin in the massive repressions of the 1930s but minimized their scale by saying "thousands of people" had suffered. Even official historians here put the figure of people killed or sentenced to labor camps by Stalin in the millions.

In his review of the Soviet Union's past, Gorbachev gave different hints at his own direction. He gave a ringing endorsement of NEP, the New Economic Policy of the 1920s that permitted limited private enterprise. At the same time, he defended the policy of collectivization in the 1930s that ruthlessly eradicated independent farming in Russia, but said that "flagrant violations of the principles of collectivization occurred everywhere."

Today, the names of several former Soviet leaders were mentioned in an official setting for the first time in decades. By talking about Nikita Khrushchev, Gorbachev rescued Stalin's successor from 23 years of obscurity. He acknowledged the contributions of Nikolai Bukharin 49 years after the party theorist was executed by Stalin. However, he attacked Leon Trotsky, Stalin's chief rival, as "antisocialist."

For the first time, Gorbachev publicly linked Leonid Brezhnev with the "stagnation" of the late 1970s and early 1980s when "the gap between word and deed widened."

But for many, the key issue in the speech was Stalin, a figure who looms largest in Soviet history after V.I. Lenin, founder of the Soviet state. For many ordinary Soviet citizens, especially war veterans, and conservatives in the current debate on history, Stalin is still a great leader who gave the country order and inspiration.

Gorbachev announced that the party would name a committee to examine the Stalin era. "This is something we have to do, all the more so since even now there are still attempts to turn away from painful matters in our history, to hush them up and to make believe that nothing special happened," he said.

"We cannot agree to this. This would be disregard for historical truth, disrespect for the memory of those who were innocent victims of lawless and arbitrary actions," he said, noting that a "truthful analysis" of the Stalin era touches on problems dealt with by Gorbachev's reform program.

But Gorbachev also dwelt on the achievements of Stalin, both during the prewar period of industrialization and during the war years. He said Stalin's "tremendous political will" was a factor in winning the war. He also defended the 1939 Stalin-Hitler pact as the only option available to the Soviet Union in the face of the Nazi threat.

"To remain faithful to historical truth, we have to see both Stalin's incontestable contribution to the struggle for socialism, to the defense of its gains, {and} the gross political errors and the abuses committed by him and those around him," Gorbachev said.

By taking the middle ground in the ideological debate over Stalin, Gorbachev struck a political compromise that is expected to disappoint many members of the intelligentsia while pleasing the conservative party establishment.

Still, his comments took the public exposure of Stalin's crimes considerably further than his predecessors. Although Khrushchev's secret speech against Stalin at the 20th party congress in 1956 reportedly was stronger than Gorbachev's, it was never published here. Gorbachev's speech, given to about 5,000 officials, foreign delegations and diplomats in the Kremlin's Palace of Congresses, was nationally televised and will be published in the press Tuesday.

"It's more than before and less than expected," said one foreign analyst. Several observers said they were disappointed by Gorbachev's measured tone, which contrasted with the increasing boldness of the historical debate in the Soviet press.

Yet others noted that the speech was not so much Gorbachev's personal statement as a political document that was approved by the full Central Committee at a meeting on Oct. 21.

According to Soviet dissident historian Roy Medvedev, the speech will release historians to touch on subjects that they had been barred from in the past. Gorbachev's mere mention of Khrushchev will restore the former leader to the history books, Medvedev said.

"In discussing these historical figures, he was in some way legitimizing them," said a western diplomat. "It may not have gone as far as some would like, but at least there are no more nonpersons, no more nonevents. That is significant."

Khrushchev became a nonperson in 1964 when he was ousted as party leader. Gorbachev today credited him with "criticizing {Stalin's} personality cult and its consequences." This, said Gorbachev said, "required no small courage."

In 1956, Khrushchev condemned Stalin for creating a "cult of personality" and proceeded to liberate 2 million to 3 million prisoners from labor camps. Millions more of Stalin's victims were legally rehabilitated, although the process was never completed.

Today, Gorbachev left unsettled the question of the rehabilitation of Bukharin, Lev Kamenev, Grigori Zinoviev and other Bolshevik leaders who were purged and executed by Stalin. He announced a commission to be named by the ruling Politburo "to make an all-round study of new and already known facts and documents related to these questions."

Gorbachev also announced this year's grain harvesting figures in the speech. He said that despite unfavorable weather throughout the country, "we succeeded in harvesting more than 210 million tons of grain.

"This was the result of strenuous efforts exerted by the people and by the party which encouraged them to work in a new way," he said.