Lev Kopelev, who emerged in the 1970s as a dissident figure of unique power and meaning for the harried Soviet human rights movement, left this country today with his wife to begin a new life in the West.

The 68-year-old author flew to Krankfurt on a one-year Soviet passport granted him recently after years of clashes with the state in defense of political and literary freedom.

Kopelev's departure and the traffic death today in Spain of exiled dissident Andrei Amalrik fell like hammer blows on the community of Moscow dissenters, already under unremitting pressure from security police and newly fearful that their cause will be discarded by the incoming Reagan administration.

The scene at Moscow's Sheremetyevo II Airport early this morning resembled a wake, with more than 40 people, few of them dry-eyed, bidding subdued farewells to the Kopelevs. Despite his wife's vow that "we'll be back," few here believe they will ever see the couple again.

Soviet authorites invariably cancel the citizenship of prominent dissidents once they have gone abroad, regardless of their behavior.

Kopelev, a barrel-chested, white-bearded survivor of Stalin's prisons, has accepted an invitation from West German Nobel Prize-winning novelist Heinrich Boell to research and write an interpretation of the image of Russia in German literature, a project he considers his "life's work."

But here in Moscow, most consider Kopelev's life's work to have been something no less important than his highly regarded literary scholarship. He and his wife occupied a unique niche in the compressed, intense world of disaffected Soviet intellectuals from whose thin ranks most of the country's modern dissenters have sprung.

Over the years, Kopelev signed numerous declarations defending individual freedoms, rigorously defended his close friend and fellow dissident, Andrei Sakharov, and lent advice and counsel and to dozens of younger writes, poets, and critics. His memoirs, "To Be Preserved Forever," and "Confessions of a True Believer," both published in the West but like all his scholarly work, banned here, are avidly read in smuggled copies.

The Kopelev apartment was a prime meeting point for artists, scientists, musicians, critics and scholars to formulate and trade ideas, argue and analyze such taboo topics as Alexander Solzhenitsyn's ideas, democracy, underground literature, and Sakharov's fate.

These are largely ephemeral matters of the intellect, but carry enormous weight and impact in the context of a society whose authoritarian leaders seek to suffocate independent thought through censorship, secret police, bureaucratic retailiation and massive propaganda.

The Kopelev apartment stood out like a beacon for these reasons, as much to the authorities as to the intellectuals. After years of trying without success to frighten Kopelev into silence, the authorities last spring expelled his wife from the Communist Party and the Writer's Union, as well as the Writer's Health and Welfare Fund. Kopelev, with a legacy of heart and liver troubles from his nine years in Stalinist camps, finally applied for exit permission this fall and received it last month.

He thus joins Vasili Aksyonov, the novelist, in that group of prominent dissenting voices virtually expelled from Soviet territory this year. Amalrik, the 42-year-old activist who died in a car crash today en route to Madrid conference on European cooperation, was similarly granted an exit visa four years ago and had been active in emigre dissident circles since. News of his death moved swiftly through Moscow tonight, casting an even deeper pall over the intellectual community.

The crowd at the airport in the morning could have as easily been found almost any normal day at the Kopelev apartment. There were children and grandchildren, novelist Vladimir Voinovich, who has also applied to leave, poets Bella Akhamadulina, Semyon Lipkin and Ina Lisnyanskaya, artists Boris Birger and Boris Messerer. Mixed into the group were several Jewish activists, several young jazz musicians, and aspirin writers of various kinds.

The Kopelevs have a daughter, Maya Litvinov, in Tarrytown, N.Y., where she lives with her husband, Pavel, grandson of Stalin-era foreign affairs commissar Maxim Litvinov. But the thought of relatives abroad did not lighten the scene.

The group watched tearfully as customs men rifled through the couples' luggage, refusing to allow them to take personal phone numbers of friends and some literary essays each had written.

And in the end, the gray-uniformed officials denied Kopelev permission to take one other possession: a small, plain wooden box filled with a few ounces of Russian earth.