WASHINGTON -- Urgently seeking a deal on President Obama's health care overhaul, Democratic senators are considering opening the Medicare rolls to uninsured middle-aged people able to purchase the coverage. 

The Medicare "buy-in" for people 55 to 64 would be available until government subsidies start flowing in 2014 to new health insurance markets designed for people who now have trouble getting and keeping affordable coverage. 

Sen. Ben Nelson, D-Neb., said the idea is on the table as part of an emerging compromise under which liberals would back away from their demand for a new government health insurance plan to compete with private carriers. Instead of a so-called public plan, the compromise envisions private insurers operating under the auspices of the government agency that now manages the federal employee health plan -- the same one that covers members of Congress. 

Also under discussion is a proposal from liberals to allow early Medicare enrollment on a permanent basis for middle-age people participating in new insurance markets called exchanges in the bill. About 30 million Americans who buy their own coverage or work for small businesses would be able to buy insurance in the exchanges starting in 2014, gaining access to a range of plans. Most would receive government subsidies. A Democratic official described the proposal on condition of anonymity because no decisions have been made. 

The Democratic negotiators -- five liberals and five moderates -- are under pressure to reach at least a tentative deal by Tuesday. The version now in the bill -- a government-run plan that states could opt out of -- is unacceptable to moderates whose votes Majority Leader Harry Reid, D-Nev., needs to pass a bill embodying Obama's signature issue. 

A companion idea also under discussion -- expanding the Medicaid program to cover more low-income people -- appears to have run into opposition from moderates. 

Republican Leader Mitch McConnell of Kentucky ridiculed the Democrats' late-innings re-engineering, and suggested adding more people to Medicare could undermine the program's already shaky finances. He called for Democrats to scrap the bill and start over. 

"Americans would rather get it right than scurry around throwing together last-minute untested experiments to get 60 votes before Christmas," McConnell said. 

Medicare now covers seniors 65 and older, as well as disabled people of any age. People in their mid-50s are among the most vulnerable to losing coverage, particularly in an economy where employers are still cutting jobs. But buying into Medicare would not be cheap. A current buy-in available to those 65 and older who don't qualify because of work history costs about $550 a month. 

Nelson said he isn't sure how much help that would be, unless new government subsidies are included. But that would raise the cost of bill. "It's always about money," he said. 

The latest public plan bears little resemblance to the original idea proposed by liberals, and embraced by Obama, during the 2008 presidential campaign. That called for the government to sell insurance to workers and their families in competition with industry giants like UnitedHealthcare. 

But instead of Medicare-for-the-masses, it would be Blue Cross Blue Shield or Kaiser Permanente, albeit with a government seal of approval from the department that handles the health plan for federal employees, including members of Congress. The Office of Personnel Management -- OPM -- would become an instantly recognizable federal acronym, like FDA and CDC. 

"It's probably the closest proposal thus far that could get the support of 60 senators. It's got legs," said Sen. Max Baucus, D-Mont., chairman of the Finance Committee. 

Negotiators worked on the compromise Tuesday as the Senate debated the 10-year, nearly $1 trillion bill. A vote on an amendment to tightly restrict abortion coverage by health plans receiving federal subsidies could also happen Tuesday. 

The possible deal has drawn a wary reaction from liberals, who support a Medicare-like approach. 

The idea being the emerging compromise is for the government to lend its seal of approval to private plans that would be offered across the nation. The plans would be available through new state insurance markets, called exchanges. New markets would create big purchasing pools for those who now have trouble finding and keeping affordable coverage -- people buying their own insurance and small businesses. Most of the 30 million consumers in the exchanges would have government subsidies to help pay premiums. 

Any insurer could approach the federal personnel office to offer a plan in the exchanges, but the plan itself would have to be nonprofit. Most Blue Cross plans are still nonprofit, as is Kaiser, the giant health maintenance organization. OPM and the plans would negotiate premiums and coverage terms.