Monsignor Lorenzo Albacete, a former scientist who became one of the most visible Catholic theologians in the United States, a defender of faith who in television appearances and newspaper commentaries addressed a complex and often doubting world, died Oct. 24 at a nursing home in Dobbs Ferry, New York. He was 73.

The cause was complications from Parkinson’s disease, said Louis Giovino, a spokesman for Communion and Liberation, a Catholic lay group with which Monsignor Albacete was associated.

A native of Puerto Rico, Monsignor Albacete came to Washington in the 1960s to study aeronautics and physics at Catholic University. Called to the priesthood, he said, he abandoned his scientific career to embark on a spiritual one. He became a theological adviser to church leaders and was known for his erudite yet approachable insights on faith.

Often, humor was his leaven.

“I used to think priests knew everything,” his mother told him, he recalled, the day of his ordination. “Now I worry,” she added, “because you are a priest and I know you don’t know anything.”

Many Americans met Monsignor Albacete through his appearances on CNN and the Charlie Rose public-affairs talk show or through his writings in The New York Times and the New Yorker magazine. He sparred with Christopher Hitchens, the learned, sometimes fulminating public intellectual who was an avowed atheist.

At a 2008 event in New York, Hitchens remarked that Christianity, with its tenets about the afterlife, was worse than the North Korean dictatorship because “you can’t get out of it by dying.” Monsignor Albacete, who said he was engaged to be married when he decided to become a priest, compared the discovery of faith with another type of life-altering encounter.

“You can’t help it,” he said. “You’ve fallen in love.”

In one essay, he reflected on the Catholic tradition of confession, a practice, he acknowledged, that many people knew as an unsettling exercise of unearthing the worst in themselves.

“Yet my experience as a confessor has had nothing to do with hearing juicy secrets,” he wrote in The Times. “Most penitents I have had repeat formulas that they learned in second grade and refer to their sins in formal categories. I have heard things like ‘I was unfaithful 23 times in deed, and about 50 times in thought.’ I remember a political exile telling me, ‘I have tortured prisoners.’ I thought, ‘At last, a new sin!’ . . . Then he really stunned me by asking, ‘Must I tell you exactly how many times?’ ”

From such episodes Monsignor Albacete drew lessons about the church and its followers.

“Confession is not therapy, nor is it moral accounting,” he wrote. “At its best, it is the affirmation that the ultimate truth of our interior life is our absolute poverty, our radical dependence, our unquenchable thirst, our desperate need to be loved.”

Amid revelations of years of child abuse within the church, he examined the “shameful situation” and the role the vow of celibacy — and its corruption — may have played in the scandal. He also expressed his conviction that the church maintained an essential role in human life.

“If, in addition to all the terrible things we have learned,” he told the New Republic in 2002, “if tomorrow it was revealed that the pope had a harem, that all the cardinals had made money on Enron stock and were involved in Internet porno, then the situation of the Church today would be similar to the situation of the Church in the late 12th century . . . when Francis of Assisi first kissed a leper.”

Lorenzo Manuel Albacete Cintrón was born Jan. 7, 1941, in San Juan, Puerto Rico. He became an altar boy over the objections of his father, whom he described as an anti-clericalist.

He received a bachelor’s degree in 1962 and a master’s degree in 1965, both in mechanical engineering and both from Catholic University, before joining the old Naval Ordnance Laboratory in White Oak, Maryland. There, he faced the tensions between science and faith.

“When I was in the lab, many people whom I deeply respected asked me how I could be a Catholic,” he told the National Catholic Reporter. “I was searching for an answer to the link between faith and reason, between nature and the supernatural.”

He returned to Catholic University, receiving a bachelor of sacred theology degree at the time of his ordination in the early 1970s. A decade later, he received a master’s degree and a doctoral degree, both in sacred theology, from the Pontifical University of Saint Thomas Aquinas in Rome. In the early years of his priesthood, Monsignor Albacete worked at the Cathedral of St. Matthew the Apostle in Washington and several parishes in Maryland.

He was associated with the Pontifical John Paul II Institute for Studies on Marriage and Family at Catholic University for a decade before leading the Pontifical Catholic University of Puerto Rico in the mid-1990s. His writings included the book “God at the Ritz” (2002). Survivors include a brother.

Monsignor Albacete was said to have had a close relationship with Pope John Paul II, whom he met as Karol Wojtyla, archbishop of Krakow, Poland, in the 1970s. Then a young priest, he sensed in Wojtyla an “intensity of . . . humanity, an energy, that, if tapped, could power the whole world,” he told the New Yorker years later.

Before John Paul II’s death in 2005, Monsignor Albacete visited the pontiff in Rome as he suffered from Parkinson’s disease.

“I said, ‘You know, Holy Father, I’m feeling a little guilty. I’ve agreed to go on television after you’ve died to say something or other about you,’ he recalled. “He smiled. . . . Then he said, ‘How do they know that I will die first?’ He was able to joke. He was not afraid.”