Lawmakers are readying for a decisive negotiating session Tuesday over the broad structure of immigration legislation, hoping one more meeting will be enough to beat Senate Majority Leader Harry Reid’s deadline.

Staff members worked through the weekend on the various titles of a draft bill, lobbyists said, drafting “pieces” of provisions — but the whole cannot come together until members reach a consensus on the big picture.

A group of Republicans and Democrats has been negotiating with the Bush administration for nearly two months but has yet to produce legislation. The key negotiators include Massachusetts Democratic Sen. Edward M. Kennedy and Republican Sens. Jon Kyl of Arizona and Arlen Specter of Pennsylvania.

Some of those lawmakers will gather again Tuesday and make a final attempt at working out several sticking points, according to lobbyists monitoring the talks.

If they cannot reach agreement, Reid, D-Nev., has indicated that he will go ahead with a vote Wednesday to cut off debate on a motion to proceed to a new version (S 1348) of last year’s Senate-passed immigration overhaul legislation.

Republicans have indicated that they will not support last year’s bill, and they will agree to proceed with the debate only if the legislation is used as a placeholder. If no deal is reached, the debate is not likely to proceed very far.

Lobbyists said Monday the broad shape of that deal is coming into focus, but it’s still far from clear how the sticking points will be worked out. A major outstanding issue is determining how family relations will factor into a proposed point system for future visas issued for new workers.

Republicans want to limit family visas to spouses and young children. Democrats have indicated that that is too narrow, and some of their allies in organized labor are supporting them on that point.

“We do oppose the attempt to eliminate the family visa category,” said Bevin Albertani, a legislative representative for Laborers International Union of North America, which represents building and highway construction workers.

Another question is whether new temporary workers will qualify for a path to legalization or whether that program will be strictly temporary.

Finally, senators will need to agree on the number of green cards made available each year.

“If there’s no path to legal residence [for new workers], we are strongly opposing the bill,” said Sonia Ramirez, a legislative representative for the AFL-CIO.

Those familiar with the talks said senators appear to be moving toward consensus on one of the most difficult issues: what to do with the estimated 12 million illegal immigrants currently living in the United States.

A general outline of an agreement would allow those immigrants to stay in the country and work legally provided that they pay fines, pass a background check and demonstrate an effort to learn English. Illegal immigrants who want to become eligible for green cards would have to wait until the federal government could clear backlogs — a process that could take up to eight years by some estimates. Even then, they could have to wait several years longer because lawmakers are considering a merit-based system for permanent residency, which could take account of applicants’ employment status, education and perhaps other factors.

But negotiations continue over whether immigrants in this subgroup could stay in the United States to apply for legalization or would have to return to their country of origin first.

Any provision that allows those currently in the country illegally to stay will draw howls of protest from the most ardent foes of illegal immigration, who will say it is an “amnesty,” even with a long timeline and conditions attached.

That could make it difficult to get 60 votes in the Senate and cause problems if the debate shifts to the House come summer.