When Watergate broke, nobody cared what Martha Mitchell knew or when she knew it except the White House, CREEP, and her husband. Early on, they had conspired to use her--Haldeman was the first to spot her possibilities as a mouth-piece--and she'd built herself quite a constituency. But now, afraid she'd speak out of turn, they were quick to discredit her: Martha was an incurable muddler. They could have trusted her, she felt, after all she'd done for Mr. President; instead, they held her ""political prisoner"" in California, and when John wouldn't even take her calls, she telephoned Helen Thomas. And that was the turning point. Freelance journalist Winnie McLendon and Martha already had a symbiotic friendship going; after John Mitchell walked out, it grew into almost full-time superintending--with the tacit quid pro quo of a joint book on Martha. (Martha stalled; this isn't it.) Rejection had always triggered the worst in her: her father had walked out too, a casualty of the Depression that robbed the Bealls of Pine Bluff (Ark.) of their position. So Martha, who had once called the press at ungodly hours because ""John Mitchell says that's. . . when you get their attention,"" now did the same whenever she was alone or afraid or incensed, and probably drinking. It's a sad story, no matter what your politics, especially when Martha lays dying in her Fifth Avenue ""Tara"" among heaps of unpaid bills, scrounging for Seconol, estranged from both husband and daughter. McLendon, preserving the quotable earmarks of the original collaboration, doesn't let sympathy get in the way of the details. And they're the best part. Randomly: Martha had capped teeth, dyslexia, diverticulitis, a son by her first husband, whom she married ""I don't know why. . . . I guess because there was competition for him."" She knew why she married Mitchell--stability, success, and other ironies. Here he's an eavesdropper like Martha, but not a mannerly one--he always interrupted, or clicked the buttons up and down. And he's a deadbeat and a heel. But the biggest heel of all is Mr. President, who for all his imperial powers couldn't--Martha rejoiced-have the name of the Kennedy Center changed. Something titillating for everyone--and more Marthas than you'd have thought.