After months of a grand jury investigation in San Francisco, a top Justice Department official said yesterday that it is unlikely that any criminal charges will be filed in the slaying of Rep. Leo J. Ryan (D-Calif.) just before the Peoples Temple massacre in Guyana.

Philip B. Heymann, head of the department's Criminal Division, said the department is leaning instead toward trying to aid prosecutions in Guyana.

Heymann said after meeting here Thursday with G. William Hunter, the U.S. attorney in San Francisco, that a case "could or might" come out of the West Coast grand jury.

But he added that cases in Guyana are "probably clearer and stronger." Thus, he said, it's likely that U.S. authorities will concentrate their efforts on helping Guyana officials get witnesses to appear in the upcoming murder trial of Larry Layton, a follower of the Rev. Jim Jones.

A team of FBI agents has spent countless hours over the past several months listening to tapes and examining records seized at the site where more than 900 cultists died last November.

They have been seeking evidence to support conspiracy charges against survivors of the tragedy who may have been involved in the murder of Ryan, who was shot after a visit to Jones' jungle camp.

U.S. authorities have said from the beginning that their chances of returning criminal indictments were slim because of the narrow jurisdiction of their investigation -- only Ryan's death -- and the deaths of witnesses and potential defendants.

Layton was charged with the murder of Ryan and four others, but his trial has been held up because the charges were filed in the wrong district. Alfred Hantman, a Justice Department attorney working on the investigation, said yesterday that the trial has been reset for this fall, and that the Guyana government is likely to ask U.S. assistance in finding witnesses.

Michael Prokes, another survivor of the Peoples Temple group closest to Jones, killed himself at a news conference in California in March. He charged that federal authorities were withholding a tape that proved that cult members weren't forced to commit suicide.

A short time later, NBC News broadcast part of a tape it said recorded the final moments of Jonestown. In it, Jones is quoted as saying of plans for Ryan's death: "They're gonna shoot that pilot and down comes the plane into the jungle. And we had better not have any of our children left when it's over, 'cause they'll parachute in here on us."

To prove a conspiracy case that would withstand challenge in American courts, Justice would have to prove that Ryan's murder was planned in the United States, rather than in Guyana.

Guyana authorities, on the other hand, have clear jurisdiction, and could charge persons for the murders of the other members of Ryan's party as well. The only U.S. law reaching the case is that against assassination of members of Congress.

The Justice Department has filed a civil suit against the Peoples Temple in an attempt to recover $4.2 million it says the U.S. government spent to remove the victims' bodies from Guyana.

Justice moved earlier to protect more than $10 million in bank accounts the cult had in Panama and other countries.Department attorneys now are seeking to have the funds returned to the United States.