A federal judge ruled here yesterday that a Washington Post reporter could not be forced to turn over to the court materials relating to a Post article published yesterday concerning the Church of Scientology.

U.S. District Judge John H. Pratt said the request, made by attorney Phillip J. Hirshkop for the church, was a "clear violation" of the First Amendment and that a subpoena for the reporter's material would not be enforced.

The reporter, Ron Shaffer, wrote in yesterday's Post that documents seized by the FBI in a raid on the church's headquarters revealed an elaborate campaign by the church to attack and discredit its enemies.

Hirshkop argued that the documents were improperly leaked to The Post by government agents who have been reviewing them. He said he did not want Shaffer to be forced to reveal his sources, and did not seek to enjoin The Post from writing future articles. He said that he merely was asking that any seized documents in The Post's possession or notes relating to the court and be destroyed.

John B. Kuhns, representing The Post, said the request by Hirshkop amounted to an "indirect way of gagging the press." Pratt agreed with Kuhns that a "qualified" reporter's privilege could be invoked by Shaffer in connection with questions about the documents, should he be forced to testify about them.

Assistant U.S. Attorney Raymond Banoun said the U.S. attorney's office would conduct an investigation in an attempt to determine the source of The Post story. But he also contended that the Scientologists themselves may have leaked the materials to make an issue in a hearing in progress before U.S. District Chief Judge William B. Bryant.

Bryant is conducting lengthy proceedings to determine whether FBI agents who carried out the search of the church's headquarters here last July 8 acted properly. To do so, he is asking the agents, document by document, how they determined whether certain material should be seized.