Washington — A vision of national party realignment appears to have faded slightly in the aftermath of the debate Sunday between President Reagan and Democratic challenger Walter F. Mondale.
Although no official in either party is speaking seriously about a Reagan defeat, talk of a Republican wave sweeping GOP candidates into Congress has suddenly subsided in the capital.
''As of today, people are not talking as much about a landslide,'' Sen. Richard G. Lugar, chairman of the National Republican Senatorial Committee, told reporters Wednesday. The Indianian argued that the mood could shift in ''two or three days.''
But for now, congressional Democrats are seizing on Mr. Mondale's strong showing as the first drink of water after a long walk in the desert. The real ''winner'' in the Reagan-Mondale debate was House Democrats, said Rep. Tony Coelho, chairman of the Democratic Congressional Campaign Committee. The ''loser'' was House Republicans, the Californian said.
The Democratic cheer is based on hopes that a more defensive President Reagan will be occupied with his own race and leave House races alone. ''The real fear was when you get the President of the United States'' campaigning personally for congressional candidates, said Representative Coelho. ''Sure, there'd be an impact.''
''The President's personal appearances in states are very important,'' confirmed Senator Lugar, who said he receives daily calls from Senate candidates hoping for a presidential visit. The Reagan campaign committee has not yet made plans for extensive congressional stumping. ''We're going to have to wait to make certain that we have our 270 electoral votes'' for the presidency, said deputy press secretary John Buckley. He said the decision would be made within 10 days about participating in Senate and House races, but that meanwhile the President was visiting only states and areas vital to his own race.
Democratic confidence that the President will bypass congressional races is premature, said Joseph R. Gaylord, director of the National Republican Campaign Committee. ''The most effective time for (campaigning for) House races is the last two weeks.''
House minority leader Robert H. Michel (R) of Illinois offered a more sobering analysis after the debate. ''If the President stayed up into (a) 20 percent (lead), it's got to have a coattail effect'' for House candidates, he said. ''If the margin is cut ... you tend to lower your sights.''
The GOP leader pointed to polls showing that increasing numbers of voters are identifying themselves as Republicans. That ''can't be wiped out by one evening's confrontation,'' he said.
But Congressman Michel also said surveys indicate that there is a Reagan handicap in House races. The GOP has discovered that it's a mistake in many areas of the country to tell voters that they should send a Republican Congress to Washington to help Reagan, said the Republican leader. ''They think there ought to be a check on the President.''
Despite Mondale's apparent success in the debate, Democratic candidates are not exactly racing to grasp his coattails, or his deficit-reduction plan for tax increases. Democrats running for the Senate ''haven't said anything about the Mondale tax plan,'' except to applaud his courage in proposing it, said J. Brian Atwood, director of the Democratic Senatorial Committee.
Mr. Atwood depicted the tax plan as a possible problem for his party's bid to recapture the Senate. In fact, the GOP already is running two TV spots tying the Democrats to a tax hike.
House candidates will continue to run independent campaigns, Coelho says. But he maintained that the Mondale debate performance means that they ''will no longer put distance'' between themselves and their party's nominee.
In the campaign of Rep. Bruce A. Morrison (D) of Connecticut, who is in one of the closest House races, workers are still leery. ''We'll wait and see,'' aide Roy Bear says. ''There are so many problems with the polls that are out there right now. Let's see what happens in the next week.''
Regardless of polls, says the aide, the Morrison campaign will aim to ''make people focus on the congressional race'' as separate from the presidential contest.
In another tight race, Rep. Thomas R. Carper (D) of Delaware is still keeping his distance from the Mondale tax plan. But according to a spokesman, the debate provided Carper with something he can embrace, Mondale's agenda for the future, which includes protecting the environment and strengthening education.