Faced with a sharp decline in the public opinion polls, Canadian Prime Minister Pierre Trudeau announced yesterday that there will be no general election this summer.

Trudeau told the House of Commons that the election, long expected in June or July, will not come until the fall or even next spring.

Opposition leaders scoffed at Trudeau's explanation, that he sensed the public would prefer that politicians stay at work in Ottawa, and said the real reason was that the polls show Trudeau's Liberals might lose an election this summer.

A Gallup poll released last week showed the Liberals and Conservatives in a dead heat, with each having the support of 41 percent of the decided voters.

"The people of Canada have been led to believe that an election was to be called and they wanted one," said Conservative leader Joe Clark. "After weeks of political game playing, Trudeau has decided that an early election is not in the interest of the Liberal Party."

Last week's Gallup Poll marked the culmination of a remarkable turnround in the seesaw fortunes of the Leberals. Last summer, the Gallup Poll showed the Liberals leading the Conservatives by 24 percentage points. Yet in August 1976, Trudeau's party was behind by 18 points in the polls.

In deciding to put off the election, Trudeau may also have been influenced by his estrestranged wife, Margaret. Since the couple separated last year, Mrs. Trudeau has toyed with a variety of lifestyles, from photographer to a jet-set habitue of the Studio 54 discotheque in New York. But now she reportedly wanrs to return to her previous role as wife of the prime minister and Trudeau may want her back. Such a reconciliation might not be possible during an election campaign.

Canada's last election, on July 8, 1974, was won handily by the Liberals. Trudeau must, by law, hold the next election within five years, or by the summer of 1969 at the latest.

But by tradition, elections are held every four years in Canada, and most observers expected such a move. The Liberals and the opposition parties had already begun tuning up their campaign machines.

But Trudeau told a press conference: "The people are not clamoring for an election."

A year ago, Trudeau was riding a wave of popularity because of this steadfast opposition to the then newly elected government in Quebec Province, which is pledged to seceding from the Canadian confederation.

But the Quebec issue has gradually receded into the background as it became clear that the province is not about to secede in the near future. That issue has been replaced by concern over the Canadian economy.This concern has heightened in recent months because of the sharp decline in the value of the Canadian dollar to less than 90 cents in terms of the U.S. dollar - the lowest level in 45 years.

While the devalued dollar brings with it many benefits, Canadians are psychologically wedded to the idea that their dollar should be worth the same as an American dollar. As the Canadian dollar fell in value, so did the popularity of the governing Liberals.

Trudeau's political standing was also hurt, ironically, by the recent election of a popular Liberal to the party's leadership in Quebec. Claude Ryan, a newspaper edition in Montreal, is considered a good bet to defeat the secessionist Parti Quebecois in the next election in the province - therby depriving Trudeau of his major issue.

Trudeau now faces the task of reviving his party's fortunes in the next few months or facing defeat at the polls.

To turn around his decline in popularity, Trudeau is expected to unveil a series of new economic and constitutional reform measures. He is also expected to do some traveling abroad in the role of a statesman and shuffle his Cabinet to bring in new blood.

But it may all be too little, too late.

"The essence of politics is timimg," said one opposition spokesman, "and Trudeau may have blown it by not calling an election last year when he was way ahead in the polls."

Trudeau could, of course, step down as leader of the Liberals and allow someone else, perhaps former Finance Minister John Turner, to take over. But when Trudeau was asked yesterday if he would step down if he thought it might help the Liberals win, he replied: "I don't think I would, no."