CONGRESS IS BACK in town, and, in addition to the big-ticket defense items and the annual appropriations crush, two important matters are on the agenda for the short session. A lot of groundwork has been done on both. What's needed now is leadership and a commitment of time so that these bills will not be lost in the rush to final adjournment.

Immigration reform is the farthest along. The Simpson-Mazzoli bill has been passed, in different forms, by both houses, and the final stumbling block is a conference to compromise the differences between the two versions of the bill. Six Senate conferees were appointed before the Republican convention. It is expected that the speaker will name 22 House conferees this week. Matters were complicated on the House side because a number of committees were involved, and the chairman of one, Carl Perkins of Education and Labor, died a few weeks ago. But staff members have been preparing tentative compromises on dozens of minor issues and devising alternatives for members to consider on the larger and more troublesome questions.

If all goes well, conferees should begin meeting early next week and, with much of the groundwork already done, they could make fast progress. Immigration reform is a tough political issue, and powerful interest groups have a lot at stake. It takes courage to vote on such a measure this close to Election Day. But legislators should see that years of study and compromise, and careful consideration in both houses, don't go down the drain.

Another important bill is on the brink of passage. The Civil Rights Act of 1984, designed to overturn the Supreme Court's Grove City decision, was passed by a whopping margin in the House and, in the Senate, only a possible filibuster threatens passage. Majority Leader Howard Baker has promised to bring the bill to the floor, and sponsors and supporters have been working during the recess to reassure wavering senators that the bill does not create any new civil rights but only restores the protections everyone thought were in place before the Grove City decision came down.

Clarifying language designed to alleviate these fears is now being worked out, and that should solidify the commitment of a majority large enough to defeat any filibuster.