Down to the wire on changes in immigration law

It may be now or never for the most sweeping immigration overhaul bill in 30 years.

The Simpson-Mazzoli bill passed the Senate in mid-August, 80 to 19. Last week it jumped a House Judiciary Committee recommittal amendment, 15 to 13.

Advocates say it would clear up chaotic conditions on the Mexican border. Hispanic immigrant opponents say it is discriminatory and unjust. If passed in present form it would impose sanctions on US employers who hire illegal aliens, it would set up an elaborate verification system to help employers determine the legality of workers, and it would legalize the status of many aliens already in the US.

The bill comes at a time when the unemployment rate stands at 9.8 percent and when estimates of illegal immigrants (chiefly over the porous Mexican border) run from 3 million to 6.5 million or more a year.

Chief enemy of the bill is time. Congress faces a midterm election, is bogged down with unpassed bills, and is summoned back to a lame-duck session in November. While many agree that something must be done about near chaos on immigration on the border the proposals in the pending bill are among the most sweeping in years. However, some pressure may have been removed by the failure of the package of right-wing so-called social legislation which has tied up the Senate in filibusters. These have included disputes over school prayer, abortion , and busing. Now it is generally agreed that these bills have been defeated for this session. Immigration-bill advocates heretofore felt the House had to pass the measure immediately, to be reconciled with the Senate version, or else it would fail for the term. Now there seems some chance the House could be asked to consider it in the post-election lame-duck session.

Differences are sharp over the pending measure whose fate may be decided this week.

''The American people want immigration reform now and they deserve a chance to see the House vote on the measure before Congress recesses,'' said Roger Conner, director of the Federation for American Immigration Reform (FAIR). He expressed ''bitter disappointment'' that some provisions have been, in his view, watered down, but nevertheless urged House Judiciary committee chairman Peter W. Rodino Jr. (D) of New Jersey to speed the measure to a vote.

On the other hand the bill is attacked by some Hispanic organizations and by industrial groups worried about penalties for employing illegal immigrants. Said a spokesman for the Mexican American Legal Defense Fund: ''Job discrimination, invasion of privacy and shattered families may face Hispanics nationwide if the Simpson-Mazzoli immigration bill passes.''

Some critics challenge proposals in the bill to allow admission of temporary workers to help harvest crops.

The Senate version of the bill limits admission of children of legal residents of Hispanic origin to the US. Another Senate amendment proclaims English the official language of the nation. Some areas near the border are currently almost bilingual, it is noted, and questions arise whether schools should be taught in two languages. Joaquin G. Avila, president of the pro-Hispanic group, charges the all-English provision is ''merely a beginning attempt to strike down legitimate bilingual services, such as government printing of street signs, emergency information and ballots in Spanish.''