A U.S. judge ruled yesterday that the government must return documents seized in an FBI raid on the Foundation Church of Scientology here July 8 because the search warrant used was unconstitutionally broad.

The raid on the church offices at 2125 S St. NW and a similar operation against Scientology offices in Los Angeles were made in connection with an investigation of alleged conspiracies by church officials. The purpose of the alleged conspiracies was to burglarize government offices, steal government property, and obstruct criminal investigations, according to court documents.

Chief Judge William B. Bryant of U.S. District Court ordered that all the materials seized here, and all copies and records of such materials, be impounded by the clerk of the court. He said the material would be returned to church officials unless the government appeals his ruling within 10 days.

The ruling applies only to the Washington raid. The Los Angeles raid is the subject of another court proceeding there.

A spokesman for the U.S. Attorney's office, which has been directing the investigation against the church here, said the office had recommended to the Justice Department that an appeal be taken.

Officials declined to comment further. If Bryant's ruling is upheld on appeal, it appears that the investigation's future is uncertain.

"The government really goofed this time," said Philip J. Hirschkop, an attorney for the Scientology church. "It was a grossly illegal search. It really proves how the government has operated with regard to the Church of Scientology."

The search warrants used here and in Los Angeles were granted on the basis of information supplied to federal investigators from a former Scientology official. The official reportedly claimed to have personal knowledge of church members who infiltrated the Justice Department and the Internal Revenue Service and stole some of the agencies' files on the church.

The warrant used in Washington listed 148 specific items that were sought. In addition, it sought other material and its final paragraph authorized agents to seize "any and all fruits, instrumentalities and evidence (at this time unknown) of the crimes of conspiracy, obstruction of justice and theft of government property . . ."

Judge Bryant ruled that this language was so broad that it amounted to a "general warrant" - authority to seize anything and everything at the discretion of the agents - and that it therefore violated the guarantee of the Fourth Amendment of the U.S. Constitution against "unreasonable searches and seizures."

The Constitution requires that search warrants list the items sought with "particularity," Bryant said. "General warrants" lack this particularity.

"The flaw I find in the warrant involved here is precisely the evil that inheres in general warrants," Bryant wrote. "The warrant in this case authorized - if indeed it did not direct - agents of the FBI to examine carefully and completely the contents of every document in the fourth-floor files of the Church and to make ad hoc, on-the-spot decisions as to which of those documents constitute evidence of conspiracy - an amorphous and open-ended crime that . . . has since its conceptual inception perplexed commentators and courts alike."

According to court records, the documents seized here include information on the personal lives of judges deciding Scientology lawsuits, files on "bugging devices" and a "locksmith course" and organizational charts of U.S. agencies.