A group of 135 West German Roman Catholic scholars, including maverick theologian Hans Kung, has issued a series of sharp challenges to Pope John Paul ii on the eve of the pontiff's visit to West Germany later this week.

The scholars called on the pope to respond to "the signs of the times" and lift the church's long-standing ban on artificial birth control, to open the dwindling ranks of the priesthood to women and married men, and to readmit divorced and remarried Catholics to the sacraments.

In a letter dispatched to the Vatican last week and scheduled to be made public in Germany on Monday, the churchmen also asked the pontiff to use his visit to this country, where the Protestant Reformation began, to make a giant leap toward Christian unity by acknowledging the "validity of the ordination of Protestant pastors and of their eucharistic celebrations" and authorizing Catholics to receive holy communion at Protestant alters and vice versa.

The letter had the backing of 25 unofficial German Catholic organizations, and of prominent authors and politicians, such as Nobel Prize-winning novelist Heinrich Boell.

One of the six challenges in the letter is a call for the pontiff to "revise the proceeding of the Roman Congregation for the Doctrine of the Faith in a way that corresponds to the principles of law and justice enshrined in [the German] state and to the freedom of the Christian, proclaimed by Christ . . . ."

Kung himself was the focus of a worldwide controversy nearly a year ago when the Vatican's Sacred Congregation for the Doctrine of the Faith revoked his certification to teach as a Catholic theologian, an action that cost him his post on the Catholic faculty of Germany's state-run University of Tuebingen. The congregation ruled that Kung failed to "conform to the doctrine" of the church, particularly in his questioning of papal infallibility.

Since then, Kung has continued to teach at the university, but in a different position. He is now on a six-city lecture tour of the United States.

Each of the challenges in the scholars' letter emerges out of their analysis of conditions in society. The lifting of the birth control ban, for instance, is proposed in the context of John Paul's often-expressed concern for the under-privileged in developing nations. "we want to encourage you to continue to commit yourself unreservevly for the poor," the letter said. "But we also know that there is a close connection in the Third World between poverty and high birth rate . . . .

"Are you prepared to revise the church's teaching on birth control in such a way as to leave [to] the conscience of the parents themselves the responsibility for the means to be used and the number of children they want?" the letter challenges.

Pope John Paul repeatedly has emphasized his support of the church's traditional birth control ban -- most recently at the Synod of Bishops in Rome last month.

In their letter, the German scholars approached the question of opening the priesthood by quoting church leaders back to themselves. "We agree with Cardinal Hoffner, president of the German Bishops Conference, that 'the most pressing problem of the postoral ministry for both parishes and bishops in the immediate future is the serious shortage of priests'."

In Germany (as in this country), the church suffers from a serious shortage of priests at a time when fewer young men ar entering seminaries. According to the scholars' letter, there were nearly enough priests to serve West Germany's 12,427 parishes in 1978, but if present trends continue, nearly one parish within a decade.

"it is obvious that upholding the legal prescription of obligatory celibacy -- which is not based on scripture, which did not hold up to the high Middle Ages in the old church and has no validity up to the present time in the Eastern churches . . . renders pointless the right and duty of Christians to come together on Sunday to the eucharistic celebration in their parish," they wrote.

The shortage of priests appears all the more ironic, the letter continued, when "there are hundreds of men and women now studying in the faculties [schools] of Catholic theology in the German Federal Republic who are ready and willing to enter the church's ministry."

In calling for more vigorous Christian unity efforts, the scholars noted that "there are very many Christians in Germany who cannot understand why -- despite the faith in the New Testament message that unites us -- historically conditioned disputed questions are kept alive and the churches continue to excommunicate one another. The division of churches is one reason why the Christian churches are increasingly losing credibility in our country . . . .

"Is it not time for the cooperation between Rome and the World Council of Churches at last to produce some practical results?" they challenged. The letter also called on the pontiff to "speak clearly -- particularly in the German Federal Republic -- about disarmament."

Reached yesterday in Dallas, where he was meeting with American biblical scholars, Kung said that many German Christians were dismayed that the pope has scheduled "only a 60-minute meeting with Protestants, there where the Reformation began."

Kung downplayed his own role in the letter from German church leaders to the pope, emphasizing that it was a group effort "to show that there is a strong part of the Catholic Church [in Germany] which thinks in a different way."

Though the Vatican sought to diminish Kung's influence in the church through its ruling last year, there are indications that the scholar remains a charismatic figure for many persons, both in and out of the church.

Just last week, the u.s. Catholic Conference published a 218-page book on the issues surrounding Kung's battle with church authorities. According to Washington Archbishop James A. Hichkey, who heads the hierarchy's committee on dictrine, the volume was publshed to illiminate the "considerable debate" generated by the Vatican action.