Roman Catholics going to mass yesterday had an unaccustomed fillup - there was a new pope to pray for.

In sermons, in the liturgy and in informal conversation after the services, the unexpectedly quick selection Saturday of Albino Cardinal Luciani, the patriarch of Venice, as the 263rd pontiff.Pope John Paul I, was at the center of interest.

Everyone was quite "delighted." said the Rev. William Norvel of the parishioners at St. Benedict the Moor parish. "Of course," he added, "they don't know any more about him than what we read in the papers."

Parishioners were not alone in their lack of knowledge about the new pontiff. Fielding a press conderence question about the policies the new pope might puruse, Belgian-born Archbishop Jean Jadot, the official representative of the Vatican in this country, responded with a Gallic shrug and a smile and said: I don't know; I've never met the man."

The archbishop, who chatted with reporters after celebrating mass at St. Matthew's Cathedral, said he felt the choice of the new pope by a group so diverse as the college of cardinals in such a short time signified that the church is "specially blessed by the Holy Spirit."

Earlier, the archbishop's statement in praise of the new pope made at the conclusion of the special 11:30 mass, produced spontaneous and prolonged applause from the congregation - a rare happening at St. Matthew's.

For some, the new pope's relative obscurity until now seemed a good sign. Speaking of worshippers at Our Lady of Victory parish, the Rev. William English, the assistant pastor, said: "I think for some, the fact that he wasn't someone the people had expected to be elected meant that it (the papal selection) may not be just a political thing - that the Lord may have been active in the choice. After all, the function of the cardinals is not just to choose a conservative or a liberal, but to choose the one the Lord wanted."

The Rev. Frank J. Bober at St. Raphael's in Rockville reported that there was "a lot of excitement" among parishioners over the fact that "he was elected so soon, and there's a lot of anticipation about what he'll be like."

Bober, like many other priests, had to scrap the sermon he had originally prepared and whip up an appropriate message about the new pope.

More than a week ago, the Catholic Women's Seminary Fund, a group favoring opening the priesthood to women, had planned a special service yesterday afternoon to pray that the cardinals would choose a pope sympathetice to their cause. They went ahead with the service, turning it instead into a service of prayer for Pope John Paul I.

As Margaret Yanta, coordinator for the group, explained: "You need to pray for a good one as well as for one who needs to change.It all comes out the same."

Although early reports seemed to indicate that the new pontiff would be no more sympathetic than his predecessor to ordaining women, Yanta said: "We don't know his growth rate - how he will respond; can be change?"

At all levels of the church, there was rejoicing that the new pope was neither diplomat nor organization man, but a bishop and pastor.

"There is a feeling among the people that they are glad he was a pastoral man - he reminded many of Pope John XXIII," said the Rev. John J. Ricard of Holy Comforter - St. Cyprian parish.

At St. Raphael's, said Bober, some parishioners commented on news reports that although Albino Luciani supported the ban on artifical contraception once Pope Paul issued his encyclical on the subject, the new pope had earlier sided with a study commission that recommended change in that position.

"They're wondering what he will do," said the priest.