You could say it's the weather, since Washingtonians have spent the last several days helping one another dig out from some 20 inches of snow. But a spirit of cooperation is undeniably stealing into the capital.
The Reagan White House and congressional Democrats, once locked in bitter partisan combat, are now aiming their shots at a common enemy - the recession - instead of at each other.
It is an uneasy truce, and it will be sorely tested soon over military spending and income taxes. But it almost guarantees that during the next few weeks Congress will produce, and the President will sign, a jobs and emergency aid bill including some $4.5 billion for jobs and relief, plus $2.9 billion for extending unemployment benefits.
House majority leader Jim Wright (D) of Texas this week called White House willingness to go along on the jobs-and-aid program ''the first sign'' that President Reagan is acting in the bipartisan manner he promised last month in his State of the Union message.
Rep. Thomas S. Foley of Washington, who heads the House Democratic task force on jobs, embraced the President's proposal as a starting point for fighting the recession. Even if joint action robs his party of a political issue, the Washington State congressman called for ''cooperation instead of confrontation.''
Mr. Foley even tried to smooth over possible conflict by promising that his party will not try to add several billion dollars more than the White House proposes.
Democrats will find it difficult to slam the Reagan antirecession plan, since it takes pages out of the Democrats' own book.
The Reagan proposal is similar to a bill that was passed last year by the House but dropped because of a Reagan veto threat. The President's package would put $250 million into emergency food and shelter and provide $2 billion for public-works projects in transportation, flood control, and national parks.
Local government grants would go up by $1.2 billion, and $765 million would go for jobs repairing veterans' hospitals, prisons, Indian schools, and other federal buildings, while $50 million would be added for day care. The President also goes along with extending unemployment benefits, due to run out in the next three months.
Democrats are not satisfied. Sen. Carl Levin (D) of Michigan, while welcoming the White House turnaround, calls it ''inadequate'' and promises to seek more aid. House Speaker Thomas P. O'Neill Jr. (D) of Massachusetts wants to add about low-income mothers and children. Moreover, Representative Foley is already talking about a second phase that would include more jobs, aid to education, and measures to deal with long-term unemployment.
But the fact that Democrats and Republicans can come together even on a first step demonstrates a changed political climate.
Two years ago President Reagan and newly powerful Republicans, many elected on his coattails, hardly needed to consult with Democrats, except for the boll-weevil conservatives who backed him. The GOP gained the Senate, and when the nominally Democratic House balked at Reagan budget and tax measures, the persuasive new President took his case to the television airwaves. Letters and calls poured in to support him.
The recession deepened, however, unemployment grew, and the federal deficit multiplied. And Democrats made a comeback, winning firm control of the House.
Now the White House is seeking out the Democratic leadership. It consults with the House speaker on jobs and meets with Ways and Means Committee chairman Dan Rostenkowski (D) of Illinois on social security problems and unemployment benefits.
Already there are fruits of the cooperation. Even before the elections last November, the White House joined Democrats to pass a historic $99 billion tax increase and reform bill to cut the federal deficit. Recently, Democrats and Republicans agreed to major social security reforms so sensitive that they would be unthinkable without bipartisan action.
The administration and congressional Democrats are negotiating over details of the jobs bill, but the basic agreement is in place.
''I think we feel a better relationship with the White House,'' said Foley this week, adding, ''Not the best, but better. . . . What I want is to continue a spirit of cooperation.''
The spirit will face a severe challenge as Congress gets to work on the 1984 budget, which bends little to Democrats who want to cap the 1983 income tax cut scheduled for next July and make deep cuts in defense spending.