Washington ? Think Medicare is a great deal? Better ask grandma first.

Senate Democrats are talking about allowing aging baby boomers into the program, but it’s far from free. Seniors now on Medicare pay an average of $4,400 a year of their own money for supplemental insurance, premiums, prescription copays, and deductibles for inpatient care and doctor visits.

That’s even after taxpayers pick up most of the cost of covering the elderly. Under one scenario Democrats are considering, people age 55 to 64 would have to pay full freight to join Medicare. Private insurance plans could well be a better deal for them.

“It’s more complicated than just saying, ‘Open Medicare up to people 55-64,”‘ said health economist Marilyn Moon, co-author of a 1999 proposal to expand the program. “In theory, it’s not a bad idea because you’re taking an existing program that works very well for an elderly population and extending it to the next group of people. But the structure of Medicare is different from private insurance.”

On the plus side, Medicare is widely accepted, with 74 percent of doctors saying they are taking all or most new patients. But many people in their late 50s are still supporting 20-year-olds, even teenage children. Would the Democrats let Medicare cover kids as well?

Medicare doesn’t offer a family plan, and it’s unlikely to under the Democrats’ plan. The program, created under President Lyndon Johnson in 1965, covers more than 45 million older and disabled people. It’s seen as a success because before Medicare about half of seniors were uninsured in life’s declining years.

But the program’s long-term financial outlook is in question, with its giant trust fund for inpatient care projected to become insolvent in nine years.

The proposed expansion is part of an effort by Senate Majority Leader Harry Reid, D-Nev., to find a compromise that can secure the 60 votes needed to pass President Barack Obama’s health overhaul plan. It would be paired with an idea to offer average Americans the option of signing up for health insurance through the same federal agency that coordinates coverage for federal employees and members of Congress.

That combination amounts to a consolation prize for liberals, facing the hard reality that the government insurance plan they wanted to create to directly compete with the likes of Aetna and Blue Cross Blue Shield lacks the necessary support in the Senate. The House bill includes a government option.

House Speaker Nancy Pelosi, D-Calif., has spoken approvingly of the Medicare expansion, without offering an endorsement.

AARP, which represents not only seniors but people over 50, is withholding judgment.

“I can’t say we support it or don’t support it until we know exactly what’s being proposed,” said John Rother, top policy strategist for the seniors’ lobby. “The positive side is that this is a program that gives you unlimited choice of doctors and hospitals, and can be run efficiently. The negative is that it’s likely to attract high-cost people, and therefore the premium payments are likely to be high.”