WASHINGTON — Nearly 60 years after the death of a government scientist who had been given LSD by the Central Intelligence Agency without his knowledge, his family says it plans to sue the government, alleging that he was murdered and did not commit suicide as the C.I.A. has long maintained.

Eric and Nils Olson, whose father, Frank Olson, was the scientist, said they plan to file a lawsuit in United States District Court here on Wednesday accusing the C.I.A. of covering up the truth about Mr. Olson’s death in 1953, one of the most infamous cases in the agency’s history.

During the intelligence reforms in the 1970s, the government gave the Olson family a financial settlement after the C.I.A. was forced to acknowledge that Mr. Olson had been given the hallucinogenic drug nine days before his death. President Gerald R. Ford met with the Olson family at the White House and apologized.

At the time, the government said Mr. Olson had killed himself by jumping out of a hotel window in Manhattan. But the Olsons came to believe that he had been murdered to keep him from talking about disturbing C.I.A. operations that he had uncovered.