THE UNHEROIC 100th Congress is half over, and a good thing too. The Democrats in control of both houses have the strength to thwart the president but not to subdue him; they sometimes lack the courage even when they have the votes. This is no longer divided government; it is isometric. The country is in stalemate. The next elections cannot come too soon.

The budget deficit is the best summation of the inability to act. The stock market loses a fifth of its value and the administration and Congress rush to respond -- with a giant placebo. The budget agreement continues the defense freeze, but that was the achievement of the previous Congress. The tax increase so painfully extorted from the president is negligible. The flimsy savings from domestic spending programs are more gimmicky or marginal than structural and real. The problem continues to be Social Security; it and the lesser programs that revolve around it account for nearly half the domestic budget, yet neither party will touch it.

The budget has been the biggest failure, but not the only one. The bills that have been passed have been mainly musts or pork -- the bailouts of the fragile savings-and-loan industry and Farm Credit System, the overrides of the president's vetoes early in the year of the highway and clean air bills left over from the last Congress. A caretaker housing bill has also been passed, and a sensibly drafted, imaginatively financed catastrophic health insurance bill will go to the president next year, as will a noncontroversial extension of the basic forms of federal aid to education. But welfare reform, which only survived on a party-line vote in the House last week, will now be weakened in the Senate. The bills bravely promised early in the year to raise the minimum wage have not been acted on by either house. Clean air legislation is stalled, as is the recycled bill to strengthen pesticide regulation. The session's main civil rights initiatives, to strengthen fair-housing enforcement and reverse the Supreme Court's 1984 Grove City decision, have yet to arrive on either floor. A proposal to limit the pig-out by which congressional campaigns are financed was filibustered to death by Republicans in the Senate.

The ultimate measure of how knotted up the government now is may be that the major achievements of the first session were things that Congress did not do, or prevented. The Senate refused to confirm Robert Bork to the Supreme Court. It kept the president from adopting threatened positions on arms control. The president and the Democrats fought to a draw on aid to the contras; it may contain the best of both positions. They seem to have fought to an unacknowledged draw on trade as well. That bill is also hung up, but mercifully.

The real problems are going to be shoved off on the next president and 101st Congress. That is the lesson of this session.