Donald J. Thorman, 52, publisher of the influential National Catholic Reporter, died yesterday in Kansas City, Mo. He had been ill for nearly a year with hepatitis, which he contracted during a trip to China.

A combination journalist, businessman and mystic, Mr. Thorman shephereded the independent, tabloid-sized Reporter to a unique role in American Catholic life.

Although circulation at its peak never exceeded 95,000 the Reporter significantly influenced the Catholic Church in this country for more than a decade.

Launched in 1964 as a spin-off of the local Kansas City diocesan paper, the Reporter distinguished itself immediately by applying the principles of tough, investigative reporting to every aspect of the Catholic Church.

With few exceptions, the Catholic press had traditionally turned a blind eye to shortcomings of the church. The emergence of the independent, inconoclastic, but well written and edited Reporter set a new standard for religious journalism by placing the church under scrutiny.

Guided by Mr. Thorman and its first editor, Robert Hoyt, the Reporter spotlighted such shortcomings at every level, vrom the Vatican to the local parish.

One of its most significant coups was the publication in 1967 of both the majority and minority reports of the papal commission on birth control. The majority argued for a change in the church's longstanding rejection of artificial contraception. But Pope Paul VI ultimately rejected that report in his encyclical a few months later, condemning artifical contraception.

Last year the paper published an extensive account of Catholic Relief Servies activities in South Vietnam, detailing improper ties between the church agency and the American military effort.

The Reporter has been equally concerned about less cosmic faults of the church, such as the case reported a few months ago of an ailing and elderly Chicago priest who had been cut off from archdiocesan health services because of a longstanding disagreement with his bishop.

While the paper was embraced by renewal-minded Catholics, it was in its early days disliked and even feared by many in positions of authority. For example, one reporter, in a routine telephone call to a New York church office, identified herself as a correspondent for the National Catholic Reporter. "Oh, My God!" blurted out the monsignor on the other end of the line, without even waiting for her question.

Mr. Thorman, who was born in Oak Park, III., was trained as a sociologist at DePaul University and Loyola University in Chicago. He also studied at the University of Freibourg in Switzerland, the University of Michigan, Fordham, Notre Dame and the University of Chicago.

He wrote or helped to write six books. His best known work was "The Emerging Layman," published in 1962, which became a best-seller among Catholic books.

He became the publisher of the National Catholic Reporter in 1965, a year after its founding. In 1971, Hoyt, who had been the founding editor, left the publication in a dispute over policy, and Mr. Thorman served as editor for nearly five years.

Since February, 1975, he has been president of the National Catholic Reporter Publishing Co., Inc., which in addition to the newspaper, publishes two newsletters, occasional books, audiovisual materials and a popular series of tape cassettes. He was also publisher of the Reporter for the past year.

The Reporter company is controlled by a self-perpetuating board of directors and is completely independent of any official church ties or financing. Circulation of the National Catholic Reporter today is about 50,000.

Mr. Thorman is survived by his wife, Barabara, and seven children.