Lyndon B. Johnson was so fearful that Hubert H. Humphrey would break with him over Vietnam in an attempt to win the 1968 election he had the FBI bug his own vice president, a new biography of LBJ discloses.

Boston University historian Robert Dallek, who has researched the life of the 36th president for the past 14 years, also reveals that Johnson, even though he had withdrawn as a candidate in March, secretly encouraged a draft-Johnson movement at the Democratic convention in Chicago that summer. He may have sought a draft for no other reason than the ego-satisfying opportunity to turn it down, Dallek writes.Dallek's book, "Flawed Giant," to be published by Oxford University Press in April, sheds new light on the pivotal 1968 election, in which Republican Richard Nixon defeated Humphrey by a hair. Nixon's election led to escalation of the war in Vietnam, more than doubling American losses there, and ultimately to the Watergate scandal and history's first presidential resignation.

Johnson had deep misgivings about Humphrey, his vice president. He "considered him too soft and too much of a bleeding-heart liberal who would have trouble making tough decisions," Johnson felt, according to Dallek.

Worse yet, in his heart Johnson also believed that Humphrey "would abandon the war the minute he took the oath of office," leaving it to history to label Johnson the first president to have lost a war, Dallek writes.

"He understood that Humphrey was under great pressure to break with him," Dallek says. "To keep close tabs on the inner workings of Humphrey's campaign, Johnson had the FBI tap Humphrey's phones. If Humphrey were going to come out against the war, Johnson wanted advance notice and a chance to dissuade him."

While historians have known that Johnson secretly taped some of his telephone conversations, the only tapes released so far have been those from the first months of the Johnson presidency following the 1963 assassination of John F. Kennedy.

Unenthusiastic about the prospects of either a Humphrey or a Nixon presidency, Johnson, according to Dallek, privately urged Republican Gov. Nelson A. Rockefeller of New York that spring to get into the race - advice Rockefeller took too late to head off a Nixon victory at the GOP convention a few months later.

Because of his distrust of Humphrey's belief in the war, Johnson secretly supported Nixon and sometimes acted to undercut Humphrey - forbidding his aides, for example, from publicly endorsing the vice president.

Johnson's ambivalence about Humphrey increased after Nixon sent the Rev. Billy Graham to play on Johnson's vanity. On Sept. 15, Graham carried word to Johnson that Nixon would give Johnson a share of the credit when the war finally was settled and that Nixon considered Johnson "the hardest working and most dedicated president in 140 years."