THE BACKSIDE of a departing Congress is always a tempting target, never more so than this year. A farm bill was finally enacted; tax reform passed the House. But the members left town without having passed an immigration bill, a Superfund bill, a civil rights bill (reversing the Supreme Court's Grove City decision, which has been a subject of legislation since early 1984), a Conrail bill, a higher education bill, a bill setting up a new retirement system for federal employees. The excuse is that the budget and deficit took up so much time. Yet the deficit was not dealt with either.

It took Congress seven months just to adopt the budget resolution -- the declaration of goals and intentions -- with which the budget process each year is supposed to start. The declaration was weak; efforts by the Senate to strengthen it -- to open the way to Social Security cuts and possible tax increases -- were defeated by the president and the House. The last months of the session were then supposed to be spent carrying out the resolution, partly by trimming appropriations, partly also by tinkering in a reconcilation bill with the underlying laws on which spending each year -- both benefits and appropriations -- is based.

This book-length reconciliation bill was the perfect metaphor for the session. It sounded more important than it was. It reached into every corner of the government -- Medicare reimbursement rates, federal pay, the tobacco program, eligibility for Aid to Families with Dependent Children and college student loans, the right to free care at veterans' hospitals. The congressional budget committees said the bill would cut the deficit by $20 billion this fiscal year and $75 billion through fiscal 1988 -- impressive numbers. But part of the $20 billion the administration had already achieved by executive order, part was fanciful accounting and only part was "real"; the bill would have left the deficit about where it found it.

And even then it did not pass. In the final hours it was put over until next year because of a breakdown between House and Senate over the use of a sales tax to finance the Superfund. A fiscal remedy was sidetracked because of a programmatic dispute; it has happened all year. Nor apparently would it have mattered if the two houses had resolved their differences. The president was waiting to veto the bill, also on assorted programmatic grounds. "From the standpoint of deficit reduction we end the year on a very dismal note," said Pete Domenici, the dogged chairman of the Senate Budget Committee.

Yet on another level it is possible to argue that this was a year of reassertion for Congress on the budget. In the defense authorization and appropriation bills and again in the Gramm-Rudman amendment to the budget process, Congress sent the president the message that he can no longer count on increases in spending authority for defense if he will not propose a way to finance them. And in fact some part of Congress' dereliction may be traced directly to an absence of commitment in the White House. But you can make too much of this. It would be a cop-out to suggest that Congress' failures are not largely of its own making.