WASHINGTON - For decades after his brothers John and Robert were assassinated, Sen. Edward M. Kennedy received many threats that he would meet the same fate, according to FBI documents released Monday.

More than 2,000 pages of partly redacted documents from 1961 to 1985 show that Kennedy, the veteran Massachusetts Democrat who died of brain cancer last year, received threats from individuals and organizations including the Ku Klux Klan, the National Socialist White People's Party, and Minutemen groups.

The files suggest Kennedy was under constant threat. About four months after Robert Kennedy was assassinated in June 1968, the FBI's Seattle office wrote an "urgent" memo to headquarters.

It discussed two anonymous letters. One predicted "assassination of Kennedy number three within twenty-four hours of the day October twentyfifth nineteensixtyeight. All Kennedy residents are in danger on that day." The other warned that "the Kennedy residence must be well protected on that date."

In 1977, an inmate who had been incarcerated next to Robert Kennedy's assassin, Sirhan Sirhan, said Sirhan had offered him $1 million and a car "in exchange for killing Sen. Kennedy." The inmate declined, the file said.

Threats persisted well after Kennedy faded from the presidential spotlight. In 1985, the Secret Service received a letter from someone in Wayne, Mich., saying, "Look, I'll kill [Ronald] Reagan and Kennedy yet, now I mean this."

The FBI analysis concluded that "the author is merely ventilating her frustrations and projecting her inadequacies."

Kennedy endured the shooting deaths of two older brothers, President John F. Kennedy on Nov. 22, 1963, and Sen. Robert F. Kennedy on June 6, 1968. Kennedy's eldest brother, Joe, had died in a 1944 plane explosion during World War II.

The FBI also looked into a rumor that "elements of the Mafia wanted to attack" the character of Edward and Robert, as well as a brother-in-law, the actor Peter Lawford, "by working through associates of Frank Sinatra to compromise them at a New York party."

On its website, the FBI calls the rumor "convoluted. . . . The FBI did not consider the rumor solid, and no other mention of it appears in the file, suggesting that the informant did not supply any corroboration to the story."

The files contain little new on Kennedy's 1969 car accident on Chappaquiddick Island off Martha's Vineyard - about 77 pages of newspaper clippings detailing how Mary Jo Kopechne, 28, died after Kennedy's car veered off a bridge into the water.

Kennedy, then 37, swam to safety, leaving Kopechne in the overturned car, and did not report the accident for 10 hours. He later pleaded guilty to leaving the scene of an accident and got a suspended sentence plus probation.

Kennedy family members were given a chance to review and to raise objections to the documents before they were released Monday, the FBI said.