They were a picture of apparent marital bliss, Pierre and Margaret Trudeau, as they appeared jointly on the platform five years ago during his successful bid for reelection.

This time the Canadian prime minister is barnstorming the country alone, but he is being dogged every step of the way by a lurid tale of men, drugs and sex told by his estranged wife.

Has he read the book? Trudeau is asked repeatedly. "The book" is Margaret's memoirs, called "Beyond Reason," which is the hottest item on the Canadian book market and a best seller after only one week.

No, he hasn't, Trudeau replies firmly.

But how did he feel knowing that everybody in his audience had read it, he was asked at a packed press conference yesterday.

"You want to know the nature of my thoughts," the 59-year-old Liberal leader retorted. "You won't get them."

The more titillating episodes from the book appeared two or three weeks ago in the Canadian press, which allocated lavish space to Margaret's escapades, including the reported affair with a unnamed U.S. senator two years ago.

Margaret, who is 30 years younger than Pierre Trudeau, describes in her memoirs both her early years, during which she engaged in a hippie way of life, and her marriage to the prime minister in 1971 that later turned sour.

It includes stormy scenes at 24 Sussex Drive, the official Ottawa residence of Canada's prime minister; Mrs. Trudeau's marijuana smoking there in front of the prime minister's security guards, and eventually her turning to other men and escapades in the United States and France.

The book's appearance in the midst of Trudeau's campaign to win a fourth term is regarded by his close associates as a potential factor in the May 22 elections.

It is code named "the X factor" and no one is sure what it could mean in terms of Trudeau's political future. But persons close to Trudeau, who speak of his deep affection for his wife, are saying that her disclosures of their troubled life have profoundly wounded the prime minister.

A senior figure in the opposition Conservative Party, Robert Stanfield, its former leader, has criticized, by implication, the first family's private life. The wife of Joe Clark, the current Conservative leader, "has got her head screwed on pretty tight," Stanfield said in a speech.

"She's a sturdy girl, a good wife for the leader of the opposition and she will make a good wife for a prime minister."

Clark and his advisers have decided to skirt the issue, apparently for fear of generating sympathy for Trudeau. Clark has decided to scrap a jingle spoofing the Trudeau marital problems that had been prepared for the election campaign.

Mrs. Trudeau's book contains a number of passages that raise questions about its preparation by her British ghostwriter, Caroline Moorehead.

When the Canadian first lady came to Washington two years ago to open a Canadian exhibition at the Smithsonian, the book says, "Mrs. Gitana," identified as the wife of the Canadian ambassador to the United States, told Mrs. Trudeau: "I have arranged for the most eligible bachelor in Washington to escort us tonight."

Apart from not identifying the man in question, the problem with this statement is that Canada never had an ambassador to the United States named Gitana.

There are other incongruities. The book calls the New Democratic Party by the wrong name and suggests that Cape Breton, which is in Nova Scotia, is in northern Canada.

Among numerous foreign dignitaries she has met as the wife of the prime minister, Mrs. Trudeau sketches a profile of Soviet Premier Alexei Kosygin-"gentle, considerate and graceful-a man whose soft eyes had a charming twinkle in them."

At the end of the Trudeaus' visit to Moscow, his wife writes how Kosygin "broke with protocol and followed me up the steps to our own territory. He understood my emotional state. Saying goodbye is never easy . . . He hugged me farewell. Both of us wept openly. In a world so full of division, political maneuvering and protocol I felt our tears were an unspoken prayer for peace and friendship."

Ironically her book seems to be the focus of greater public attention than any of the weighty issue that face this 112-year-old Canadian confederation.

Throughout this period, Trudeau has publicly maintained his composure, as a man who was deserted by a woman and left with three small children to take care of.

There is considerable sympathy here for such a concerned father and criticism of his wife, who is frequently described in the press as an "empty-headed twit." But one also hears views that "a man who cannot manage his own house cannot be expected to manage the country."

William French, writer for the Toronto Globe and Mail, in assessing Mrs. Tudeau's book placed it in the following context:

"This is a nation of sanctimonious tut-tutters who have a deep need to point an admonishing finger at something or someone. Usually it is the United States we are smugly self-righteous about, but at the moment they don't have a war we can condemn, so Margaret fills our needs." CAPTION: Picture 1, MARGARET TRUDEAU; Picture 2, PIERRE TRUDEAU, There is considerable criticism of his wife, who is frequently described as an "empty-headed twit" but one also hears views that "a man who cannot manage his own house cannot be expected to manage the country."