All of the Peoples Temple members still sought for the fatal assault on Rep. Leo J. Ryan (D-Calif.) and his party in Guyana are now known to be dead, federal authorities said yesterday.

Larry Layton, the only one of nine alleged participants still alive, was formally indicted on murder charges in Guyana yesterday.

Five of the others had already been identified among the bodies flown to the United States. There was still a vague hope that one or more of the remaining three might still be living and someday available for prosecution or testimony

It was hoped they might be able to shed new light on the advance planning that went into the Nov. 18 attack, which apparently helped touch off the forced mass suicides in Jonestown.

That hope is now gone, further complicating the government's efforts to determine if a conspiracy, possibly hatched in the United States, led up to the Ryan killing.

Little concrete evidence of such a conspiracy has been uncovered, according to federal sources, after examination of hundreds of documents and interviews with hundreds of Peoples Temple members and associates.

The questioning yesterday shifted to a federal grand jury room in San Francisco, where returning Temple survivors are being interviewed under oath.

The Justice Department convened the grand jury hurriedly, to catch Temple members while their memories are fresh and before they scatter to other parts of the country.

Investigators are known to be especially interested in the activities of a Peoples Temple operative who was dispatched from Jonestown. Guyana, in early November with instructions to infiltrate a group of concerned relatives and find out what the Ryan party's mission in Guyana was to be.

Tim Carter, a top lieutenant to Peoples Temple leader Jim Jones, has told The Washington Post that he did indeed carry out his mission successfully.

Posing as a Peoples Temple defector, Carter said, he investigated Ryan's plans and returned to Jonestown three days before the Ryan party arrived there on its inspection tour.

Federal investigators are trying to determine what, if any, connection Carter's trip had with the disastrous outcome of the Ryan visit.

Carter, who is still detained for questioning in Guyana by local authorities, has said he was allowed to leave Jonestown during the forced mass suicides. He said Maria Katsaris, the camp treasurer and a mistress of Jones, told Carter and two others to "get out before it's too late," and handed them a revolver and a suitcase full of money.

The eight dead suspects were identified yesterday as Thomas D. Kice, 43; Wesley Karl Bridenbach, 18; Ronald Deval, 23; Robert E. Kice, 30; Joseph L. Wilson, 24; Albert A. Touchette, 24; Ronald W. Talley, 33, and Eddie Crenshaw, 23.

Arrest warrants for all eight, taken out a few days after the Jonestown tragedy, were formally dropped yesterday by the U.S. attorney in San Francisco.