Los Angeles ? Two former presidents and the widow of Lyndon B. Johnson are calling on the History Channel to investigate a documentary it aired alleging President Johnson was involved in the Kennedy assassination.

Lady Bird Johnson said the film “falsely and irresponsibly” accuses her husband of conspiring to kill President Kennedy.

No accusation made against Johnson “has hurt as painfully,” the 91-year-old former first lady said in a Jan. 29 letter. Her husband died in 1973.

Copies of her letter were sent to the chief executives of three companies that own A&E Networks, which includes the History Channel. The letters went to Bob Wright of NBC, Victor Ganzi of Hearst Corp. and Michael Eisner of The Walt Disney Co.

Presidents Ford and Carter also sent letters citing the documentary, “The Guilty Men,” which aired last November as part of a series of History Channel specials on the Nov. 22, 1963, assassination.

Ford, noting he was the last surviving member of the Warren Commission that determined Lee Harvey Oswald acted alone in killing Kennedy, called the History Channel documentary “reprehensible.”

Alleging that Johnson, as Kennedy’s vice president, was part of a conspiracy to murder him is “the greatest, most damaging accusation ever made against a former vice president and president in American History,” Ford, 90, wrote in his Jan. 23 letter.

The letters were released Monday by Tom Johnson, chairman of the LBJ Foundation.