THE bipartisan agreement on Central American policy, announced Friday, came not a moment too soon. Not so much for Central America, where it represented little more than a belated adjustment of United States policy to political reality. No, the important impact of the agreement was in Washington, where something, anything, that could be presented as good news was badly needed both on Capitol Hill and at the White House.

These past few months have not been easy for the executive or the legislators. Much has been made of President Bush's supposedly slow start. Indeed, he has seemed at times to be fading away. Mr. Bush's appearances on the evening news, one of a President's tools in shaping the public agenda, have been declining steadily since his triumphant inaugural, said Robert Lichter, who monitors television news coverage at the Center for Media and Public Affairs.

But the Congress has done no better. Many members say this has been about the rockiest opening of a session that they can remember. It is not just that little has been done, but that what has been done has been most unpleasant. ''About all we've done is kill the pay raise and John Tower,'' said Senator Bob Dole, the Republican leader. In January and February, Congress met less and passed fewer bills than in the same period in 1981, the last time a new President and a new Congress arrived together.

The Democrats have promised an agenda of their own, but they have been slow in moving it. The House Speaker, Jim Wright, is embattled by an ethics inquiry. The new Senate leader, George Mitchell, is just getting his sea legs as he tries to keep his promise of wider consultation with his colleagues. Only in recent days have the Democrats begun action on one of their big items: an increase in the minimum wage. But there is still no agreement with the White House, and the President is threatening a veto if the Democrats stick to the increase they want.