Washington — Despite having to knuckle under to a Republican president in Washington, Democratic congressmen are looking forward to modest gains in 1982 home district races.
A change for the better in the Democrats' prospects can be read both in the air here and in hard numbers, according to strategists in both parties.
The Democrats still lack a new, positive theme that could serve as a focus for their campaigns. But largely gone are the defeatism and dismay - the unfamiliar helplessness before the Reagan-GOP congressional juggernaut - that marked the first three-fourths of this year for the Democrats.
GOP congressional campaign spokesmen still publicly claim that Republicans can take control of Congress in 1982. Privately, however, they are scaling down their hopes.
''The way things are going now, Republicans might break even in 1982 - but I doubt it,'' says Richard Bennett, a New England pollster with ties to the Republican Party.
President Reagan still holds a working majority in the House, despite the Democrats' numerical edge. Two dozen or so Southern Democrats continue to cross over to the Republican side of the aisle, where the GOP members have been voting as a solid bloc on key economic issues.
But the Democrats see a longtime pattern - the president's party loses seats in midterm elections - prevailing again in 1982.
The Democrats are holding their edge in party affiliation. According to the latest Gallup poll, 45 percent of Americans are Democrats, 27 percent Republicans, and 28 percent independents. In another Gallup test, the Democrats lead the Republicans 53 percent to 47 percent in a trial test of how congressional elections would go if held now.
Only twice in the last half century - in 1946 and 1952 - has the Republican Party won more seats in the lower house than the Democrats, observes George Gallup. And the chances of this happening in 1982 look slight now. The GOP's biggest hurdle appears to be in the South. When asked ''Which party would you like to see win in this congressional district?'' 60 percent of Southern voters picked the Democrats, 40 percent the Republicans. Outside the South, the GOP runs almost even with the Democrats.
A number of other factors are working in the Democrats' favor. Redistricting - redrawing congressional lines after the 1980 census, shifting seats from the industrial states to the growing South and West - will more likely mean the Republicans will pick up less than half the 10-seat gain they had been predicting, Republican sources concede.
Rep. Tony Coelho (D) of California, chairman of the Democratic Congressional Campaign Committee, goes further. ''I predict we [Democrats] will have at a minimum a 10-seat gain in 1982,'' he says.
Mr. Coelho talks colorfully of a ''Darwinian theory'' of 1980, meaning that only the politically fit Democrats were reelected. ''If you survived 1980, you're a hardy Democrat,'' he says. ''If you're a Republican who won in 1980, you're warming a Democratic seat.''
Ted van Dyk, president of the Center for Democratic Policy, makes a similar point. ''Mathematics is more important than anything else,'' Mr. van Dyk says. ''Those House Democrats who were in marginal seats lost theirs last time. The Republicans in marginal seats will lose them in '82.'' In the 1982 Senate races, the numbers favor the Republicans: Twice as many Democrats as Republicans are up for reelection.
President Reagan's theatrical victories on the budget and taxes - like his veto showdown last week - will have little impact on House races, say these analysts.
''It makes him look strong and in charge,'' van Dyk says. ''It might have an impact in a presidential year, where there might be more of a rub-off. But in a midterm race like '82, the races will turn on the local candidate's honesty, personality, not on whether the President appears to be strong or Congress weak.''
''The economy will likely trend back favorably after the midyear point, so Democratic candidates will not likely be able to count on an easy ride from that ,'' van Dyk says.
But van Dyk also sees the GOP ranks splitting over social issues such as abortion and school prayer.
Also looming next year is a major debate on nuclear weapons and the US power balance with the Soviets, van Dyk says.
Such a debate could run several years. ''Can the President enhance the peace and preserve it will be the issues,'' van Dyk says. ''This is not just a question of war for people now. They see it's a matter of being blown up. The heaviest mail, by far, congressmen are getting now has to do with war and peace.''
So far, the current congressional preoccupation with the economy, with the President pulling the strings, has been unusual, and confusing for voters. Incumbents, most of whom are Democrats, can be expected to take advantage of the confusion.
''This is a very atypical Congress,'' says Thomas E. Mann, executive director of the American Political Science Association. ''The number of votes is down. Budget matters in the House have always fostered sharply partisan battles. That's all we've had - budget battles.''
''What goes on in Washington sets the tone and tenor of next year's campaigns ,'' Mr. Mann says. ''But the basic fact remains that congressional elections are localm elections.''