If the polls are right, Prime Minister Joe Clark's Conservatives are heading for defeat in Canada's general election Monday.

The 40-year-old Clark still hopes to pull off a Harry Truman and confound the predictions the way Truman did when he beat Thomas Dewey in 1948.

But Clark's backroom handlers, who publicly talk a brave game and go through the motions, concede privately that their own polls match Gallup and other public polls. These show Clark's Progressive Conservative Party trailing 13 to 15 points behind Pierre Trudeau's Liberals.

There is an air of confusion and anxiety in the Conservative camp. Clark a relatively obscure westerner who was propelled to the country's highest office eight months ago, stands in danger of becoming a footnote in history books. The harder the fights in the closing days of the campaign and the more he is exposed to the public on phone-in TV and radio shows, the more he sounds like a young man apprenticing for a job.

The anger among Conservative Party workers is based on their apparent expectation of the defeat to come. After 16 years of Liberal rule they had finally managed to seize power only to witness an inexperienced Troy leadership practically hand back the government to the Liberals again.

Although Clark is well liked within the party, he is already the subject of private sniping by senior Conservative Party figures. The extraordinary thing about this campaign is that Clark himself has emerged as his party's key liability because he is widely perceived as a weak and indecisive leader -- an image that is somehow ampliphied by his multiple chin, shaky hands, awkward manners and plainness.

Columnist Allen Fotheringham ascribes this image to the fact that Clark has never held a job and has spent his entire life in politics. "Most 40-year-olds today are products of a very laid-back, casual background," he said. "The 40-year-old Joe Clark has spent his life since high school in a political incubator. He is out of sync with his times. His manner is coming from another era and so not fitting his youth."

The only other clear issue is a highly unpopular 18 cents per gallon tax increase on gasoline which Clark proposed as part of a belt-tightening budget. The Liberals joined by the socialist New Democratic Party brought his minority government down on this issue last December.

Clark is now criticized by Conservatives for failure to count or court votes in the House of Commons before submitting the budget. Some argue that he could have delayed the vote to make a deal with the tiny Social Credit Party that would have given the Conservatives a chance to stay in office until summer.

A Gallup poll in mid-January showed the Liberals getting 49 percent of the popular vote with the Conservatives getting 28 percent and the socialists 20 percent.

Clark's response to the Soviet invasion of Afghanistan and the excitement at the exploit of the Canadian Embassy in Tehran in rescuing six Americans have distracted attention from domestic concerns. The latest polls show a drop in the Liberal lead but not sufficient to indicate a turn of the tide.

The shift toward the Liberals comes less from any enthusiasm for Trudeau than from a profound disappointment with Clark. To many Canadians he just doesn't seem like a prime minister. Indicative is a series of demeaning Joe Clark jokes that have become fashionable throughout Canada.

Clark has recognized the problem and in the final week of the campaign had sought to meet it head on. He argued that he needed "a fair chance" to demonstrate his abilities and complained about what he called "quite a job done on me in the early days."

He's trying, he says, to "turn attention away from the image that has been created" to the job he had done as prime minister. "I'm a better man than Pierre Elliot Trudeau," he declared Monday.

In his public speeches the Conservative leader argues that he wants to put Canada on the road to energy self-sufficiency and to straighten out its debt-ridden finances. He does not want to play politics and has "no illusions about what role my charisma plays," remarks that prompt chuckles from listeners.

But as he meandered about the country and engaged in face-to-face conversations and interviews, Clark's natural politeness and diffidence placed him at a disadvantage. He could not obscure a sense of foreboding that his career was seriously imperiled and he repeatedly engaged in the type of postmortem analyses of what had gone wrong during the past eight months. He did not realize until the very last minute he said, that the Liberals really intended to bring him down in December.

Such defeatist talk coupled with the spectacle of an incumbent government begging the electorate for fairness has produced an air of unreality in the Conservative camp.

By contrast the Liberal campaign cry blazoned across every bus stop in the land is that "Joe Clark had a chance -- it is time to give Canada a chance."

Except in the past few days when he has loosened up sensing victory the 60-year-old Trudeau has been programmed by his party to read from a text that is usually vague and tepid in everything except in ridicule of Clark.

To avoid potential traps for some sort of a verbal altercation that could upset the polls, the Liberals have kept Trudeau away from the public and the press in an effort to avoid reminding voters why they voted against Trudeau last May. "They have Trudeau wrapped in plastic and on a short leash," columnist Christopher Oung said.

Although it is a cynical strategy, it apparently has been successful. But as a result the subjects of Quebec, national unity and badly needed constitutional changes, all of which deal with the basic problems in the country, have not been mentioned during the campaign.

Trudeau made vague statements and very few campaign promises. He attacked Clark's controversial 18-cent gasoline price increase as excessive without saying what he would do about enenergy prices. The thrust of the entire campaign was to focus on public doubts about Clark's ability to run the country.

This campaign, said the Toronto Star recently, "may mark the movement at which we agree collectively to end the pretense that issues make any . . . difference."

Commented the Ottawa Journal, "The Canadian political process is in very bad shape if governments are to be elected on the basis of a man's laugh, or his walk, or a habit of drumming his fingers on a tabletop."