Ono of the most hotly contested issues before Congress in the closing days of the last session will be back within a few weeks. The Simpson-Mazzoli immigration reform bill was approved by the Senate in 1981. It was passed in different forms by both houses in the last session, but the clock ran down before conferees could agree on a compromise. The subject is a tough one. While national opinion polls consistently show broad support for immigration reform, well-organized opponents, each objecting to a specific provision, have been able to stall final action.

For example: some businessmen don't like having to screen job applicants about their immigration status; western growers object to limitations on the immigration of agricultural workers; some Hispanic groups believe that all workers with Spanish surnames will suffer discrimination. Groups that opposed the bill for different reasons have been able to prevent passage in two Congresses.

The problem hasn't gone away, of course. Sponsors have been regrouping and revising the proposal. Sen. Alan Simpson's staff has drafted a new bill that reflects some of the lessons of the last session. They believe the paper-work burden on employers can be cut, for instance. The new draft would reduce record-keeping and adjust fines so that first offenses could be treated leniently and subsequent violations penalized more heavily. Some provisions of the bill relating to deportation adjudications have been accomplished by administrative action in the Justice Department; other sections changing conditions for legal immigration will be dropped so that the focus of the measure will be squarely on employer sanctions and amnesty.

Some groups that opposed employer sanctions but wanted amnesty for illegals will be disappointed by the draft. Two out of three Americans oppose the legalization of those who entered this country without documents, and the new bill may reflect that opposition by delaying amnesty until a committee certifies that illegal immigration is under control. Hispanic groups took a gamble that they would lose ground on the generous amnesty provision by delaying passage; their work will be more difficult this time around.

First drafts are made to be revised, and this one surely will be. Sen. Simpson will be talking to opponents and supporters, to House leaders and administration officials, to Republicans and Democrats, seeking to build consensus before a bill is offered. Much depends on his counterpart in the House, Rep. Roman Mazzoli, and on House Judiciary Committee Chairman Peter Rodino. The legislators who have assumed this burden and carried it for three Congresses deserve credit and support. The job is unpopular, but it is critically important that it be done.