Suspicious that Hubert H. Humphrey would deviate from the administration line on Vietnam in hopes of winning the 1968 election, Lyndon B. Johnson had his vice president's telephone bugged to keep tabs on him, a new LBJ biography discloses.

In his heart, Johnson believed that Humphrey "would abandon the war the minute he took the oath of office," which meant the Communists would win and Johnson would be labeled in history as the first president to have lost a war, Robert Dallek writes in "Flawed Giant," to be published next month by Oxford University Press."He understood that Humphrey was under great pressure to break with him," Dallek writes. "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."

Historians have known that Johnson secretly recorded some of his phone conversations; tapes from 1963 have recently been made public. But Dallek's book, which is based on interviews with former Johnson and Humphrey aides, offers the first evidence that Johnson went so far as to wiretap Humphrey's phones in the vice president's office.

Dallek, who has researched the life of the 36th president for 14 years, also reports that Johnson worked secretly to initiate a draft-Johnson boom at the Democratic convention in Chicago during the summer of 1968, even though he had announced in March that he would not be a candidate. Johnson's own unpopularity - and the antiwar rioting in Chicago that prevented him from even visiting the convention city - squelched the plan.