Philadelphia Inquirer reporter Ralph Cipriano sued his editor yesterday, a move so unusual that no one could think of a precedent.

Cipriano is seeking at least $50,000 plus punitive damages from his newspaper, parent company Knight-Ridder Inc. and the Inquirer's editor, Robert J. Rosenthal, for what the lawsuit calls "false and defamatory statements," "innuendo" and "malicious libel."

The dispute stems from Cipriano's decision to write an investigative piece on the local Roman Catholic archdiocese for the National Catholic Reporter after contending that the Inquirer refused to publish much of his material. Rosenthal told The Washington Post in a June 13 article that on the subject of the church, Cipriano "has a very strong personal point of view and an agenda. . . . There were things we didn't publish that Ralph wrote that we didn't think were truthful. He could never prove them."

Those remarks, the lawsuit said, "destroyed the reputation of Ralph Cipriano in that a reasonable reader would infer that Ralph Cipriano is dishonest and engaged in unethical and illicit conduct." The Associated Press followed up and gave the story national distribution, the suit said.

Inquirer spokeswoman Pamela Browner said that "we disagree with Ralph because we believe our coverage of the Archdiocese of Philadelphia has been fair, accurate and relevant. We regret that Ralph has chosen a lawsuit as his means of addressing the matter of how the Inquirer covers a topic of great interest to our readers."

According to the suit, Rosenthal said at a June 30 staff meeting that his remarks to The Post were a "blunder."

In a letter to The Post published July 22, Rosenthal said his paper had already carried much of what Cipriano wrote for the National Catholic Reporter. He said he "should not, however, have described as untruthful some of the material Mr. Cipriano wrote that we did not publish. I should have said he told us things as he was reporting that he had not substantiated, and that we would not, of course, publish them until they were substantiated."

Reached in the newsroom, Cipriano, an 11-year Inquirer veteran, declined comment. But his attorney, James E. Beasley, said Inquirer editors recently sent Cipriano a letter warning that his work is unsatisfactory and that he may be subject to future discipline or discharge.

Cipriano indicated in June that he had trouble getting the Inquirer to publish documented allegations of mismanagement by Cardinal Anthony Bevilacqua, who he said "was a sacred cow at my newspaper." Bevilacqua has assailed Cipriano for trying to "unjustly malign the Catholic Church."