-- Even by the standards of the Nixon White House, the plan to blow up Washington's preeminent think tank seemed crazy, presidential counselor John W. Dean III recalled here today.

But there was White House aide John Ehrlichman on the phone one day in 1971, telling Dean that "Chuck Colson wants me to firebomb the Brookings [Institution]." Describing the incident to several hundred presidential history enthusiasts at the John F. Kennedy Library and Museum, Dean said he was dumbfounded.

"I said, 'John, this is absolute insanity,' " he remembered. " 'People could die. This is absurd.' "

Dean, who served four months in prison for his role in the Watergate coverup, spun the story casually -- just another believe-it-or-not revelation from the annals of a dark and complicated presidency -- at a two-day conference on the effect of White House taping systems on seven 20th century presidents.

The practice began in 1940 with Franklin D. Roosevelt, who said he wanted to make sure he was quoted accurately in the media. White House taping ended in 1974, after thousands of tapes exposed illegal and unethical activities that led to the demise of Richard M. Nixon's presidency.

In a panel discussion, Dean recounted the day he told Nixon there was "a cancer on the presi- dency" -- a phrase linked with the corruption of Watergate.

Dean said Nixon was careful even with his most trusted aides to guard his involvement in the scandal.

"When I first started dealing with Nixon, I wasn't sure how much he knew," Dean said. "I now know he knew far more than I was ever aware of."

Dean was disbarred in 1976. He lives in Beverly Hills, Calif., and works as a writer, lecturer and private investment banker.

As for the proposed bombing of the Brookings Institution, Dean said Colson floated the idea as a way to retrieve certain documents Nixon wanted that were housed in the research center not far from the White House. Colson suggested that while firefighters were trying to douse the damage caused by a bomb, White House operatives could rush in and seize the papers.

It seemed incredible, but now that he has listened to earlier tapes, Dean said he has heard Nixon "literally pounding on his desk, saying, 'I want that break-in at the Brookings.' "