CEDAR RAPIDS, IOWA -- The tall man, impeccably clad in a crisp white shirt, rep tie and dark gray suit, swung into his peroration to about 50 supporters who had paid $50 each for a cocktail reception with him in a big new private home here.

"We're exactly where we want to be. We're in the perfect position to make the tide rise here next February and the leverage you have in Iowa is enormous," Pierre S. (Pete) du Pont IV concluded enthusiastically.

"Gary Hart finished second here with 16 percent of the Democratic vote in 1984 and, in effect, he won. I've got 5 percent of the Republican vote here now."

Du Pont paused for effect. "You know, we may have peaked too soon."

Critics tell du Pont that he is a hopeless longshot for the 1988 Republican presidential nomination, that people may like him one-on-one but won't waste their vote on him because they consider him unelectable and that several of his positions are too radical.

He runs at the very bottom of most national and Iowa polls, despite his earliest-ever formal announcement in 1986, and even some of his supporters fear his year is not 1988. "His time may be down the road a few years," one said. "This just may not be his year."

However, the former Delaware governor and member of one of the nation's wealthiest families is undeterred. He is aiming to finish third in Iowa and New Hampshire and then go into the southern regional primary on "Super Tuesday," March 8, as the conservative alternative to Vice President Bush or Sen. Robert J. Dole (R-Kan.).

"I've to to beat somebody, Jack {Kemp} or George or Bob," he said. "If I don't do well in Iowa and New Hampshire that's the end of it, but if I do the rest will come together. We're starting to organize in the South but it all depends on these first two."

To this end he contends that he has spent more time in Iowa and New Hampshire than any other Republican candidate, about 60 days in Iowa and 50 in New Hampshire since he formally announced 13 months ago.

Du Pont's scenario has changed somewhat recently, however.

"Until recently we assumed it would be a Bush race, but now I think my opponent is going to be Dole," du Pont said the day after Bush formally announced. "Dole is likely to upset Bush in Iowa and then it'll be du Pont against Dole and I think I'm going to win that. I like the feel of it."

Du Pont brings some substantial talents to his task. Despite his patrician bearing and name -- one observer described him as having the first name of a snooty French waiter and the last name of a robber baron -- he is an affable and attractive one-on-one campaigner, which is a big asset in the small-town, small-crowd retail politics of Iowa and New Hampshire.

No coffee shop patron or hardware store customer in Iowa and New Hampshire is safe from looking up and having a pleasant-voiced stranger introduce himself as a presidential candidate, pull up a chair and launch into his proposals for farm subsidy and Social Security reform.

Du Pont, who is running a dark-horse's low-budget campaign, tells his audiences that, "I've become one of the most conservative candidates in the race. Not because I've changed but because the others have moved to the left."

His opponents scoff that du Pont is an opportunistic, come-lately conservative who had a standard eastern, moderate Republican voting record as a House member in the 1970s and tailored his views to the political climate. Du Pont counters that he is where he is ideologically because of his eight years of grappling with Delaware's severe economic problems when he was governor.

"I'm the only one of the dozen presidential candidates in both parties who is talking about issues that matter to people and that everyone in America knows have to be addressed," he said.

In Iowa City, at the sort of reception that is the heart of campaigning in the Iowa caucuses, du Pont outlined the five issues that are the basis of his campaign to an audience of Republicans, most of whom were shopping for a candidate. His proposals are:Phase out all farm subsidies over five years and return the farmer to the free market system. He said the $26 billion spent last year on farm supports only causes overproduction without helping ailing farmers.

Conduct mandatory random drug testing in all high schools and withhold driver's licenses from those who fail.

Give everyone the option of opening private savings accounts to augment Social Security, which du Pont contends is necessary to reduce future claims of the "baby boom" generation and save the system from bankruptcy.

The taxpayer could subtract the amount he puts into his private account each year from his income tax bill. He will get a reduced Social Security payment on retirement in proportion to the size of his private account, but according to du Pont this will be more than offset by the income from the account. The taxpayer would continue to make full payments into the Social Security system, which will keep it funded.

Force the public schools to improve by giving vouchers to parents who want to send their children to private schools.

Require every able-bodied welfare recipient to take a job and have the government create jobs for them when necessary.

"Right now we're forcing families to break up in order to be eligible for welfare checks. Any job is better than just sitting around the house drawing a check," he said.

Du Pont also enthusiastically supports aid to the Nicaraguan contras and President Reagan's proposed Strategic Defense Initiative (SDI).

Probably none of the Republican candidates has violated the GOP's "11th Commandment" against speaking ill of any Republican more than du Pont.

He is critical of all his GOP rivals for being too timid to talk about reforming Social Security, the farm program and welfare. He has intimated that Dole is a "hypocrite" on these issues and has accused Bush of being an administration "lackey" who has spent the last seven years in a "cocoon."

Although some opponents concede du Pont gets good marks with voters for the courage of his proposals, others contend they are too radical for GOP voters and are a desperate attempt to get attention.