With just over two weeks to go in the campaign, the midterm congressional elections of 1982 have the makings of a landslide that may never occur.

The Democratic Party is prospering in public opinion polls from economic hard times, with 60 percent of the voters now saying they want to send a Democrat to Congress. But even the party's own leaders doubt that those numbers will translate into sweeping gains in the House or Senate. The strength of Republican candidates in many marginal races, the girth of the GOP bankroll, and the absence of a compelling Democratic alternative to Reaganomics has led professionals in both parties to project "normal" Republican losses in the House and a small net change in the Senate.

They hedge this by saying that the undecided vote remains high in many marginal contests -- as it often does until the eve of a midterm election -- and if a decisive trend develops late, it is far more likely to break for the Democrats.

Otherwise, both Charles T. Manatt, chairman of the Democratic National Committee, and Richard Richards, chairman of the Republican National Committee, are predicting a Democratic gain of 12 to 15 seats in the House, a figure in line with the normal gain a party makes two years after losing the White House.

A special Washington Post-ABC News poll of 27 of the most tightly contested congressional races in the country shows that the Democrats could pick up seven or eight seats in those races alone. Analysts believe the Democrats must do that well in such races to make significant gains nationwide.

A Republican loss of 15 seats in the House would jeopardize President Reagan's working majority of Republicans and conservative Democrats. A GOP loss of 25 seats or more could stalemate the Reagan administration. At present, the Democrats' House majority is 241 to 192, with two vacancies.

Each party predicts it will gain one to three seats in the Senate, where the Republicans' present lead is 53 to 46, with one independent who is retiring. The Democrats must defend 21 of the 33 Senate seats up for election this year, creating long odds against recapturing control of the Senate, even in the rosiest of Democratic scenarios.

Republicans face the likelihood of more severe losses in the major governorship races, however.

The eight most populous states in the nation are electing governors this year, and the Republicans currently hold five. Their goal at the beginning of the campaign had been to hang onto four, but that now seems unlikely.

Most Republican professionals appear resigned to losing governorships in Ohio and Michigan, where incumbents James A. Rhodes and William G. Milliken are stepping down.

The Republicans feel confident about the reelection of Pennsylvania Gov. Richard Thornburgh, and are expressing hope these days that two-term Illinois Gov. James Thompson will be able to withstand the challenge of former senator Adlai E. Stevenson III.

But they see little chance of unseating Democratic Gov. Bob Graham in Florida. The contest in California between Republican Attorney General George Deukmejian and Democratic Mayor Tom Bradley of Los Angeles and the New York race between Republican businessman Lewis Lehrman and Democratic Lt. Gov. Mario Cuomo are both considered uphill gubernatorial battles for the GOP.

The closest governor's race, and the one that could decide whether the Republicans hold onto their minimal gubernatorial power base going into the 1984 presidential elections, is in Texas, where one-term Republican Gov. Bill Clements is being pressed hard by Democratic Attorney General Mark White.

The congressional races across the country present a tableau of opportunities not fully exploited by the Democrats.

With unemployment over 10 percent and bankruptcies at post-Depression highs, the "out" party should be looking at a jackpot on Nov. 2.

But the Democrats aren't. They blame this on money. The Republicans cite message.

"If the Democrats had a program they could sell in a heads-up way, I think we'd be in real trouble," said Richards, the lame-duck Republican national chairman.

"But they're still running against Herbert Hoover."

Democrats acknowledge they have been short on constructive or captivating themes. "It would be disingenuous to deny it," said top Democratic National Committee staff aide Bernard Aronson. He claimed that ideas are indeed bubbling forth from the party: education for high technology, public jobs for rebuilding the infrastructure of roads and bridges, tax streamlining, trade fairness. But they lack the clarity and sweep of candidate Reagan's 1980 appeals to "get the government off our backs," and they are having a tougher time working their way into the national political dialogue.

Meantime, the Democrats' congressional candidates have been mostly content to attack Reaganomics and leave it at that.

"The campaigns are much more tightly focused on the president's economic policies than I would have expected a few months ago," said Leon Billings, director of the Democratic Senatorial Campaign Committee. "It's a case of the candidates being educated by the voters."

Billings said he believes that the attacks are just now taking their toll. His evidence: Republican incumbent senators with supposedly safe leads in Indiana, Delaware, New Mexico and Vermont have in the past week begun attacking their opponents. In politics, the axiom is that challengers attack, incumbents stay positive. "These are the tactics of people who've seen data suggesting their position is eroding," Billings argued.

The Democrats' list of possible gains in the Senate has lengthened this month. At the beginning of the fall, they were most hopeful of toppling Sen. Orrin Hatch (R-Utah) and Sen. Harrison Schmitt (R-N.M.) and taking the open seat in California.

Now they have cooled somewhat on the Hatch race, but believe that their challengers have credible chances in Missouri, where state Sen. Harriett Woods has pulled even with Republican Sen. John C. Danforth, according to a poll published last week by the St. Louis Globe-Democrat, and in Minnesota, where department store heir Mark Dayton has laid out more than $4 million of his own money against Republican Sen. David Durenberger.

The Democrats also believe that their challengers, though still behind in the polls, are within striking distance of Sen. Robert T. Stafford in Vermont, Sen. John Chafee in Rhode Island, Sen. William V. Roth Jr. in Delaware, Sen. Malcolm Wallop in Wyoming, and Sen. Lowell Weicker in Connecticut.

The Republicans, naturally, paint a far different picture as both sides posture to obtain a shower of late money from political action committees.

Sen. Bob Packwood (Ore.), chairman of the Republican Senatorial Campaign Committee, predicted last week that his party would lose none of its incumbents and capture up to three Democratic seats.

He said that San Diego Mayor Pete Wilson has a 10-point lead over Democratic Gov. Edmund G. (Jerry) Brown Jr. in the California Senate race, and challenger Larry Williams has pulled ahead of Democratic Sen. John Melcher in Montana. There also are good chances for GOP pickups in Virginia, Nevada, Mississippi and Ohio, he said.

If it turns out that Republicans do suffer some Senate losses, it won't be for want of money.

Their three major party committees raised $161 million in the first 18 months of the campaign, compared to $25 million for the Democrats. This money has financed a $15 million national media campaign urging voters to "stay the course" with Reaganomics, and it will enable the GOP to funnel sizable contributions to marginal House and Senate races.

In Maine, for example, the open-seat House race between Republican John McKernan and Democrat John M. Kerry is on everybody's target list: as of the end of last month the Republican had raised $259,279, the Democrat, $152,849. In Connecticut, Republican Nancy Johnson has a 2-to-1 funding edge over Democrat William Curry in a closely watched open-seat race.

The pattern is the same throughout the country.

In the roughly 80 House races considered marginal, Democratic challengers are heavily outspent by Republican incumbents, Republican challengers are not nearly as outgunned by Democratic incumbents, and the GOP has the fund-raising edge in open seats.

Democratic Congressional Campaign Committee Chairman Tony Coelho (D-Calif.) thinks the money gap is preventing his party from being competitive in "10 to 12 races." These are what the party pros call "second tier" challenge races, where the Democrat is down but, with enough money to get a message across, could catch a tide and win.

In these final weeks, Coelho will try to find and finance four or five such races. "For me, it's going to be a matter of hoping I guess the right ones; it's going to be like finding the needles in the haystack," he said. "The Republicans can just cover the whole stack."