Theologian Hans Kung was giving a series of lectures at the Protestant Riverside Church in New York City last year when Cardinal Karol Wojtyla was chosen pope.

To the many requests for comment on the new pontiff, Kung replied only that he did not know him. Two days later, on a plane trip to Washington to keep a lecture appointment, the theologian pressed intensely for the subtlest nuances of detail that had been trickling in on the news wires about the new man in the Vatican.

Kung's obvious concern about the new pope's stance on doctrinal matters seemed out of character for a world-renowned theologian who had twice ignored summonses from the Vatican's Holy Office [now known as the Sacred Congregation for the Doctrine of the Faith] saying: "The question is not who is right but what is right."

Yesterday's Vatican action declaring Kung quilty of heresy, which constitutes a direct threat to both his teaching career and his livelihood, may explain why he was concerned.

The tall, wavy-haired priest, who usually lectures in a business suit, immaculately groomed, reacted to the Vatican condemnation of him yesterday in typical fashion: he vowed to fight it.

"As a Catholic theologian, I will continue to stand up for Catholics and fight so that this step will be revoked," he said.

"I am ashamed of my church," he continued, and called it scandalous that "inquisitional trials were still conducted in the 20th century" in a church that bases its teachings on Jesus Christ.

"It is very saddening that German cardinals and bishops collaborated in this inquisition," he added.

Kung is the eldest of seven children of a prosperous Swiss shoe merchant. He studied philosophy and theology at the Gregorian University in Rome, the Sorbonne and the Catholic Institute of Paris. He was ordained in Rome in 1954.

In 1962 he wrote a book, "The Church, Reform and Reunion." Later that same year he traveled to Rome for the opening of the Second Vatican Council. Before it was over four years later, the bishops of the church worldwide had instituted many of the reforms he had proposed.

But Kung continued to press on the outer edges of Catholic thought and belief. He challenged the doctrine, established by the First Vatican Council in 1870 that the pope was infallible when speaking from the chair of St. Peter. He tried to rethink how present-day Christians could best understand the ancient creedal formulations that Christ is both human and divine.

He supported the opening of the priesthood to women and opening the Catholic Church's holy communion to other baptized Christians.

In the 15 years since the Second Vatican Council, the Roman Catholic Church worldwide has struggled to assimilate the reforms and changes made there.

But nearly three years ago, Kung was the moving force behind a unique gathering of theologians at Notre Dame University. Their theme: Vatican III: The work that needs to be done."

Kung's doctoral dissertation was on the theology of the giant of Protestant theology, Karl Barth -- highly unusual for a Catholic in 1939. Barth himself wrote a preface when the book was published. The study contributed both to Kung's later commitment to ecumenical Christianity and to the conviction expressed subsequently by the Sacred Congregation that Kung's writings were "too Protestant."

While the Vatican speaks of Catholic doctrine as a "deposit of faith," never changing, Kung advocated an ancient Catholic principle of the church as always in need of reform.

Kung also contended that in founding the Catholic church and giving authority to Peter and the other disciples, Jesus in no way envisioned the monarchial structure that subsequently emerged in the Roman Catholic tradition. He assailed the concept of infallibility on both historical and rationalistic grounds. "How can you prove you are infallible?" he challenged. r"You must already be infallible to do that."