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.