PRAGUE -- After years of grass-roots growth, Czechoslovakia's Roman Catholic Church has mounted a new campaign to strengthen its legal position and seems close to winning concessions from Prague's Communist authorities.

For the first time in almost four years, representatives of the government are negotiating with the Vatican on the appointment of new bishops for the country's 10 dioceses with vacant posts. No new bishops have been appointed here since 1973.

At the same time, Communist authorities have been forced to react to a petition drive that church officials say has collected 300,000 signatures in support of greater freedoms for the church. The popular campaign is one of the most extensive independent initiatives in Czechoslovakia since the Soviet invasion of 1968.

So far, government officials have made no concessions to the church, and officials on both sides said the two rounds of negotiations held so far in Czechoslovakia and at the Vatican have not produced concrete results.

However, with another round of talks due to begin soon at the Vatican, there is hope here that the new Communist leadership of Milos Jakes will compromise with church authorities rather than risk the possibility of protests from western governments or demonstrations in the country. An estimated 9.9 million Czechoslovaks are Catholics -- 60 percent of the population.

Government officials project a mood of optimism. "We would like to solve a large complex of problems, not just one or two individual cases of bishops but much more," said Vladimir Janku, director of the government secretariat for church affairs and a chief negotiator with the Vatican. "From our side, we have a lot of good will to find solutions."

The situation of the Catholic Church here is particularly significant because Czechoslovakia has been at once a focus of a recent revival of religious faith in Eastern Europe and the site of what Pope John Paul II recently labeled the harshest anticlerical repression on the continent.

Building on a long tradition of state regulation of religion in Czechoslovakia, Communist authorities here have persisted in a Stalinist-style strategy of seeking to establish direct party control over bishops and force the gradual shrinking of the church's presence long after such tactics were abandoned by neighboring Poland and Hungary.

At the same time, the state's repression, combined with the church's image as a spiritual alternative, has helped attract large numbers of new followers to the church during the 1980s, especially among young people.

Church activists said the new dynamism, manifested more clearly than ever in the petition drive, is the principal force moving authorities toward concessions. "The psychological moment is important," said Vaclav Maly, an activist priest stripped of the government license that all clergy here are required to have. "The authorities are nervous, because they are faced for the first time with a mass of people ready to defend their rights."

Another factor in the church's new position has been the increased assertiveness of its leader, Cardinal Frantisek Tomasek of Prague, and his evidently strong backing by the Polish-born pope. Tomasek gave the petition drive a major boost early last month by releasing a letter to Catholics calling on them to make their voices heard by state authorities to show "how the problems of church-state relations should be solved."

The petition, which church officials said was first drawn up by a peasant and church activist in Moravia, lists 31 demands, the first of which is for the separation of the church and state. At present, the state controls all church property and finances, licensing priests and paying their salaries.

The initiative has seemed to gain momentum because of the renewed negotiations between the Vatican and Prague that began late last year after two bishops died, leaving the country with only the 88-year-old Tomasek and two resident bishops in their late seventies.

At the root of the 15-year-old impasse over the empty seats is a Communist Party effort to increase the its control over the clergy through a Communist-backed organization, Pacem in Terris. Nominally a peace movement for clergy, the front has been banned by the Vatican, but Czechoslovak authorities have insisted that at least some of any new bishops should be drawn from its members.

In the last round of negotiations, Janku reportedly offered to accept church nominations for two bishops if the Vatican would agree to name the head of Pacem in Terris, Frantisek Vymetal, to the bishop's post in the Olmouc diocese. Although the Vatican accepted a similar trade-off the last time bishops were named in the early 1970s, the government offer was turned down.

It is unclear whether the government will be willing to relax its position. Janku said in an interview that he is not insisting that new bishops be members of Pacem in Terris, but he added that the group's members "can't be discriminated against."

Janku also dismissed the petition, denying that it won widespread support or that he had even seen it. An article in the party daily Rude Pravo this month bluntly attacked Tomasek's support for the initiative, saying it "put him in a quite delicate situation."

Still, church activists said they are convinced that their movement has gained a momentum that will force the party to change.

"The first step will be the naming of three or four auxiliary bishops," Maly predicted. "The Communists are testing the Vatican officials to see how tough they are. But they {the Communists} will give in, not out of good will but because they want to avoid new troubles with the West and with the people here who are waiting for their response."