Religious faith in the Soviet Union is reviving slowly in a land where state-imposed atheism has long held sway.

But it is a slow emergence, and the church hierarchy is cautious.As evidence that the atmosphere is changing, church, state and party officials cite the return to the church of the 13th century Danilov Monastery, the promise of a new law relaxing Stalin-era restrictions on worship and the release from prison and labor camps of religious dissidents.

The dissidents cautiously agree. Still they have asked President Reagan to join them in prayer Wednesday for an estimated 200 people they say still are prisoners because of their beliefs.

Reagan, in a visit to Moscow's oldest monastery Monday, paid tribute to the Orthodox faith that next week will mark its 1,000th anniversary.

"Religious life still is strictly regulated by the Stalinist legislation on cults, which deprives us of the possibility of uniting in religious community without barriers, to own houses of worship, study and distribute the Bible, and teach our children in Sunday school," seven religious dissidents said in a statement to Reagan.

"We ask you to give us the great honor of your presence at a joint prayer for the freeing of prisoners of faith," they said.

Dissidents, led by former political prisoners Father Gleb Yakunin and layman Alexander Ogorodnikov and others, also seek recognition for the underground Ukrainian Catholic Church and return to the Orthodox Church of the Pechersky monastery in Kiev, the country's oldest.

Reagan told monks at the Danilov monastery that he hoped the church bells silenced by repression might someday be "clamoring for joy in their newfound freedom." He did not say whether he could accept their invitation.

He expressed the hope that Ukrainian Catholic believers and others might soon be able to openly practice their faith.

Orthodoxy, for centuries the dominant faith of Russia, was closely identified with the czarist government and suffered severe repression after the 1917 Bolshevik revolution.

Tens of thousands of churches were destroyed or converted to government use, priests were exiled or killed, and in 1927 under dictator Josef V. Stalin authorities passed strict laws prohibiting charitable activities, religious education of the young and requiring registration of all religious organizations with the government.

Those strictures remain in force today.

In a meeting with Patriarch Pimen of Moscow and All Russia on April 29, Soviet Communist Party leader Mikhail S. Gorbachev criticized the "tragic developments" of the Stalin years and promised to ease restrictions on the church in the new legislation that is being developed.

Pimen pledged "full support to . . . the architect of perestroika and the herald of new political thinking." The meeting between the ailing church leader and Gorbachev, the son of a religious farm woman, was the first of its kind since 1943.

There is no official count of believers in the Soviet Union, but the number is thought to be in the tens of millions, perhaps as many as 90 million including Jews and Moslems.

Besides the Orthodox church, Soviet Christians include Eastern Rite and Roman Catholics, and Baptists, Pentacostalists and other Protestants.

The majority of churchgoers still are middle-age or older, but young people are increasingly attending services. Orthodox priests say they receive many requests to be baptized by young people who know little about the faith, but are searching for something to give meaning to their lives.