VILNIUS, LITHUANIA, U.S.S.R. -- The narrow, cobblestone street flanking the brown walls of the Dominicans Church here had the atmosphere of an outdoor coffee hour one balmy recent Sunday as Catholic worshipers, leaving a late-morning service, lingered to mix with easy informality.

Across the river at the Church of St. Raphael, proud parents encircled a private photographer who distributed pictures of a ceremony at which 30 young people had taken their first communion. In the parish hall, a priest offered a visitor a videocassette of Pope John Paul II's visit to neighboring Poland, home-recorded from Polish television.

These Sunday vignettes suggest how life in Lithuania's Catholic Church, once haunted by fear and official Soviet repression, has gradually attained a semblance of normality. Yet even as they mark the 600th anniversary of Lithuanian Catholicism this year, church authorities say it is unclear whether the reform policies of Kremlin leader Mikhail Gorbachev will significantly brighten the church's long-term prospects.

For now, they say, the people of this relatively prosperous and traditionally religious Baltic republic are discouraged by Gorbachev's refusal to allow the pope to attend their anniversary celebration. "Glasnost is helping, it is an influence, but it hasn't really touched us yet," said one of Lithuania's seven Catholic bishops, who asked not to be named, referring to the Soviet word for "openness."

The trend of official policy toward Lithuania's church is particularly significant because Roman Catholicism here not only is stronger than anywhere else in the Soviet Union, but also is linked to the coherence and self-expression of the Lithuanian people as a nation.

Pope John Paul II has conditioned an improvement of relations between Moscow and the Vatican in part on better treatment of the Lithuanian church.

That the church here has broad popular support was demonstrated June 28, when the principal celebration marking the completion of Lithuanian Catholicism's sixth century was held in six Vilnius churches. Tens of thousands of faithful, many of them young people, overflowed the huge old buildings.

At the stunning baroque Church of Sts. Peter and Paul, thousands of people spilled outside the walls and blocked traffic on the busy circle as they marched around the church singing hymns, participants said. "It was cold and raining that day but the people came anyway," said a priest. "There was a tremendous feeling of joy and togetherness."

Church leaders cite the official handling of the anniversary events, including the absence of police regulation of the euphoric crowds, as one of a series of small signs of possible improvement in church-state relations. To mark the anniversary, a state publishing house issued a high-quality book with color pictures of 150 Lithuanian churches, and a number of foreigners -- although not the pope -- were allowed to visit Vilnius for the event.

In Klaipeda, Lithuania's port city on the Baltic Sea, authorities announced last month, without warning, that they would hand back a large church that the state had seized and turned into a concert hall in 1960, right after it was built. The action followed years of grass-roots campaigning by Catholics, who once collected 140,000 signatures on a petition demanding the church's return.

Over the past four years, Moscow has gradually allowed the Vatican to fill gaps in the church hierarchy with the nomination of four new bishops and has authorized the only Catholic seminary, in the city of Kaunas, to increase its entering classes of would-be priests to 30 a year.

Criminal prosecution of citizens for being involved in underground Catholic publications, such as the 15-year-old Chronicle of the Lithuanian Catholic Church, ceased after 1980.

The church has also benefited from improvement in relations between the Soviet Union and Poland, which governed Vilnius from 1920 to 1939. Beginning last year, when Soviet authorities eased restrictions on travel between Poland and Lithuania, tens of thousands of Poles have crossed the border to visit relatives among the large Polish minority in the Lithuanian Republic, and priests have come to see the churches that are part of the shared heritage of Lithuania and Poland.

Three of the 11 functioning Catholic churches in Vilnius have Polish-language services and one, Dominicans, uses Polish exclusively. One priest said that as many as 10 Polish priests are visiting in Vilnius at any one time. Many of the Polish clerics stay for one or two months and deliver sermons at the Polish-language services, he said.

As a result, much of the Catholic community in Vilnius has recently had access to the bolder ideas and more open practices of the powerful Polish church. "Almost every family has had a visit from Poland," said a young construction engineer active in Vilnius' Polish community, "so we all know what is going on there."

Still, priests and activists are quick to point out that the church here, unlike the church in Poland, has yet to crack the basic scheme of state repression or achieve a measure of independence or stability.

Because of state-imposed enrollment limits, the church has been unable to train enough priests at the Kaunas seminary to replace those who have retired or died, and the number of priests decreased from 708 in 1980 to 665 last year. There are 150 churches with no regular priests, and two dioceses have no bishops.

The government still holds historic churches it seized in Vilnius and Kaunas, and does not permit the construction of new churches.

In Kaunas, the pre-World War II capital of the independent state of Lithuania and still the seat of the Lithuanian church, the church offices are in a crumbling tenement alongside a huge, stately church seized by the state and converted into a movie theater, complete with a garish marquee.

Changing this environment, said one of the bishops, would require a fundamental shift of political policy. "It is clear that things are not getting worse," he said. "It is better. That is a fact. But the ideological question, the underlying attitude toward the church, has not been addressed. The question for us is when or if that will happen."

For many in the church, the key test of Gorbachev's intentions may be his dealings with the pope. Many here hope that John Paul II will be invited to the Soviet Union next year for the 1,000th anniversary of the Orthodox Church and will be allowed to visit Lithuania.

"People here are very expectant," the bishop said. "They really want to see the pope. The problem is that it is out of our hands. We here cannot bring that about. We can only be patient and hope that the future will bring us real change. Without that hope we can't live."