WASHINGTON – A scaled-back Medicare prescription drug benefit proposal gained momentum Friday, picking up support from the nation’s largest lobbying group for the elderly.

“We’re going to support it,” said William Novelli, executive director and CEO for the AARP. “We think this is the best we can get for our members. It’s a framework to go back and work on.”

The compromise plan would help mostly low-income elderly or those who have already spent a significant amount of money on medicine.

Sen. Edward Kennedy, the chairman of the Senate’s health committee, conceded that the measure was gathering steam even though a group of senators continues to try to hammer out a more comprehensive plan that would provide coverage for all senior citizens.

“There are those that believe we need a down payment of some form or shape even if it has to be a catastrophic proposal,” Kennedy, D-Mass., said. “Certainly, I think at this point, the majority of Democratic members feel that way.”

But Sen. Olympia Snowe, R-Maine, one of the senators working on a more expansive plan, said lawmakers were giving in too soon. “There’s no reason to go with a lesser plan. It’s a cop-out,” Snowe said, adding that a more comprehensive plan was still “doable.”

Kennedy predicted the scaled-back plan would get bipartisan support. Final details were being worked out by Sens. Bob Graham, D-Fla., and Gordon Smith, R-Ore.

“This new bipartisan plan will help all seniors buy prescription drugs but it will give the greatest help to the most vulnerable older Americans, those with lower incomes and with the most serious health problems,” said Graham.

Smith said, “This is a good, focused plan that all of us should be able to support.”

The compromise is a retreat from Democrats’ longtime push for a comprehensive benefit that covers all senior citizens. But it also omits Republicans’ push to have a plan that relies on private insurers. The compromise calls for a benefit administered through Medicare, according to one Senate Democratic aide, who spoke on the condition of anonymity.

The proposal would cost an estimated $400 billion over 10 years and would cover about half of the 40 million senior citizens on Medicare, Kennedy said. That’s substantially smaller than the $594 billion plan Democrats unsuccessfully brought to the House floor earlier this week. That plan, as well as a $370 billion proposal offered by a coalition of Republicans, a Democrat and the Senate’s lone independent, failed to get the 60 votes necessary for passage.

A group of Republican lawmakers offered a $160 billion plan that was also targeted to the poorest seniors and those with high drug costs, but that plan failed as well.

The compromise proposal is substantially different from that measure.

Seniors with incomes below 150 percent of the federal poverty level would get full coverage with nominal co-payments, according to Senate Democratic aides. All other seniors would receive government help of 5 percent of the cost of each prescription drug, although aides said additional discounts could be provided through group purchasing power.