MAJOR IMMIGRATION reform legislation was reintroduced last week, and The New York Times promptly dubbed the proposal the "Simpson-Nobody bill." Earlier versions of the measure had been offered in the last two congresses by the bipartisan, bicameral team of Sen. Alan Simpson (R-Wyo.) and Rep. Romano Mazzoli (D-Ky.). Sen. Simpson is alone this year -- temporarily, we hope -- in offering the new proposal, a somewhat modified version of the bill that has passed the Senate twice before.

Has Mr. Mazzoli deserted the cause? That's doubtful, but his party seems to be in disarray over how to proceed. House Judiciary Committee Chairman Peter Rodino has long been a leader in immigration legislation, and it is possible he wants to take the lead in the House this year. There is also a rumor that Rep. Mazzoli, who voted to seat Republican candidate Rick McIntyre in the bitter dispute over the vote in the 8th District of Indiana, has been warned by other Democrats that they will seek revenge by blocking legislation that bears his name. This is a deplorable tactic, but it might explain the Kentuckian's reluctance to become the prime sponsor of the new bill. In any event, House Democrats should get their act together in support of a proposal in this area of great national interest and importance.

Sen. Simpson's new bill makes some concessions to the business community, which had objected to the record-keeping provisions of the earlier bills. The proposal also pulls back on the generous amnesty offered before, by delaying implementation until a commission certifies that illegal immigration is, in fact, reasonably under control. In a concession to the Reagan administration, the bill sets a cap on what the federal government would have to pay states, which will bear the heavy financial burden of providing services to newly legalized immigrants.

These changes in the bill should lock in the support of the Chamber of Commerce and the administration, and may even win a few votes among those who opposed the original, immediate amnesty. That's good strategy on the part of Sen. Simpson. But what about legislators who preferred the old bill with its more generous amnesty? They have an obligation to enter the debate if they want to be part of the solution. What is the response of the Democrats?