Mary Pinchot Meyer was the product of a world of advantage as lush and lazy as the pre-World War I world of Edith Wharton. After graduating from Vassar, she married Cord Meyer, a war hero and idealist committed to world government. In Burleigh's account he became soured and embittered in the course of his C.I.A. years, and after her divorce she became ''a well-bred ingenue out looking for fun and getting in trouble along the way.'' She had several affairs, dabbled in drugs with Timothy Leary and ended up having trysts with Kennedy at the White House. ''Mary was bad,'' said a friend.

It gives an odd sense of deja vu, after recent Oval Office revelations, to be reminded of the raunchy, frat party atmosphere of the Kennedy White House. The country saw images of Pablo Casals playing the cello in the East Room; the typical behind-the-scenes gathering seems to have been something out of ''Animal House'' -- a cheerful drunk putting his foot through Jackie's birthday gift to her husband of a priceless lithograph; Phil Graham, the publisher of The Post, splitting his trousers doing the twist; Ted Kennedy somehow ending an evening with one pant leg ripped away.

Here Mary Meyer found her identity, Burleigh writes. Sleeping with Jack Kennedy conferred on a woman ''a certain power,'' and it suited Mary Meyer just fine. In some of the details, the story of Meyer's affair with Kennedy reads like a reprise of the Bill and Monica Show. We are told, for example, of Meyer's frequent visits with Kennedy in the White House while Jackie was away, and even about a journalist confidant named James Truitt, who betrayed many of her secrets to National Enquirer -- including a story about Mary forgetting her slip after one visit and having it mailed back to her in a sealed White House envelope.

Mary Meyer was, by all accounts, no bubblehead. She had endured the tragic death of a son and the suicide of a half sister and, at the time of her death at the age of 44, was trying to become a serious artist. But there is no proof at all that she played a significant role in cold-war history, and this, combined with the fact that anyone who knows what her diary contained isn't talking, leaves us with a book that is filled with speculation and sometimes feverishly overwritten.

The chapter about Ray Crump's trial is the best part of ''A Very Private Woman.'' He was defended by a black lawyer named Dovey Roundtree, a woman worth a book of her own. Roundtree's defense leaps from the page, as she pounds away at the formidable circumstantial evidence while clearly not forgetting for a minute that liberal whites in the rapidly changing civil rights environment were afraid of appearing to be part of a lynch mob. Acquittal came two weeks before the Watts riots, when, Burleigh writes, the privilege of Mary Meyer's liberal friends ''had become an albatross of white guilt and their neighborhood a place to be defended.'' (Crump subsequently racked up a horrific life of crime.)