Just as Sen. Edward M. Kennedy (D-Mass.) has begun stepping up preparations for another possible run at the presidency, a biography of his ex-wife has been published that may draw unwelcome attention to his personal life.

The book, "Living with the Kennedys/The Joan Kennedy Story," portrays Joan Kennedy as a wronged wife battling to overcome alcoholism, and Kennedy as a philandering, distant husband whose only use for her during his 1980 presidential campaign was as a political ornament.

The Kennedys began living apart in 1976, became legally separated in 1981, and were divorced in 1983, ending a 24-year marriage. The book focuses on the events of 1980, when Joan Kennedy campaigned for her husband and hoped to bring about a reconciliation.

The biography -- described as written without Joan Kennedy's cooperation or approval -- is by Marcia Chellis, Joan Kennedy's administrative assistant from 1979 to 1982. It was published two weeks ago by Simon and Schuster, and early sales are reported brisk.

"I couldn't help but think that if it becomes any kind of best seller, it's going to raise Kennedy's negatives all over again," said a top Democratic National Committee official, who asked not to be identified. "Ted is like the Tar Baby in the Uncle Remus story. He just can't get free of this stuff."

Kennedy's press secretary, Robert Mann, said the senator had no comment on the book. Other Kennedy aides, past and present, played down its potential impact on his political fortunes.

"I think there's a certain public tiredness with the subject," said Robert Shrum, an ex-press secretary and consultant to Kennedy's political action committee. "People who hate the Kennedys believe this kind of trash already, and I'm not sure other people care anymore."

Despite a promotional campaign that hints otherwise, the book is not written in an expose motif. It contains no "smoking guns" -- no explicit accounts of Kennedy's private life that might be hurled at him by future political opponents.

On the other hand, it hardly flatters the senator. It contains general references to his past marital infidelities, and it suggests that his womanizing is what drove his insecure wife to drink.

The book portrays Joan Kennedy as a fragile but courageous woman who used the challenge of the 1980 campaign to motivate herself to overcome alcoholism, and Kennedy as an aloof figure with scant interest in his wife's struggles. At the time, they had been estranged for three years and Kennedy was raising the three children.

After Kennedy's famous speech to the Democratic National Convention in New York, for example, he asked his wife to join him for a private lunch the following day, Chellis writes. It was an unusual request. Joan Kennedy spent that morning brimming with excitement, hoping against hope that this might mean their marriage could be saved, Chellis writes.

But when the lunch took place, it turned out to be in the company of the national press corps, just another "media event" to show off a gallant candidate and supportive wife, the book says.

Chellis, who notes in the book that she, too, is a recovered alcoholic, has been criticized for violating the confidence of her former friend and employer.

"I haven't heard anything about this book from my political friends," said Rep. Barbara A. Mikulski (D-Md.), a Kennedy supporter in 1980. "What I do get is a lot of people shocked at the breach of a relationship. It was my impression during 1980 that Marcia was sort of a buddy to Joan, helping to sustain her, getting her past her drinking problem. What someone says to someone else in those relationships ought to be confidential."

Kennedy aides concede that the "character" issue raised by Chappaquiddick and by books like Chellis' will always hurt the senator with a slice of the electorate. But they say they hope that, with time, the numbers diminish.

They note that Kennedy shows up well in presidential polls this year. A midsummer survey by Gallup had him tied with Vice President Bush in early 1988 trial heats, 46 to 46 percent. More importantly, Gallup put Kennedy's "highly favorable" ratings among voters at 27 percent and his "highly unfavorable" ratings at 7 percent.

On the other hand, Kennedy led in almost all presidential opinion polls throughout the 1970s, only to drop dramatically in public esteem once he became a candidate in 1979. It was not until the end of that primary challenge against President Jimmy Carter, when Kennedy had been reduced to the status of a protest candidate, that his numbers began to rise again.

After sitting out the 1984 presidential race for family reasons, Kennedy is now beginning to make noises about 1988. This fall, he has been meeting with journalists and political supporters, assuring them that he intends to run. He has lost weight. He has instructed his political action committee to cull and update his national political network.

Privately, some of his old supporters say his time has passed. A prominent one, Rep. Barney Frank (D-Mass.), said so publicly this summer, arguing that Kennedy has spent so many years as a lightning rod for conservative attacks that he no longer stands a chance of being elected president. "Barney is suffering from liberal fatigue," groused Shrum.

Kennedy, meantime, is busy retooling -- hanging onto his liberal ideals but trying to shape them to the realities of the 1980s. In March at a speech at Hofstra University, he suggested that economic growth, rather than direct government intervention, may be the surest route to social justice.

In a speech prepared for delivery Friday at Bard College in Red Hook, N.Y., but not given in person due to Hurricane Gloria, Kennedy expanded on that theme.

"In my view, the political pendulum is ready to swing -- if progressives will give it a push in the right direction. Americans are ready for a new era of public activism -- not an era in which we repeat the past, ratify what has been done before, or restore every program -- but an activism which addresses the great issue of modernizing our industries and our economy . . . .

"We must deal with the budget deficit. We must reform taxes to encourage growth instead of distorting and misdirecting it. And we must form a new partnership of government, business, and labor to shape and carry out a new strategy for economic growth."

But even as Kennedy fine-tunes the message and kick-starts the political machine, some of his old hands concede that his fortunes ultimately may turn on matters not broached in any speech or mitigated by any endorsement.

"I think there's a hope that time will smooth out some of the rough edges around him," said one former Kennedy aide. "But I don't think anyone has any illusions that you can present him as a new and unsullied candidate."