Medicare is a $310 billion federal program serving 42 million Americans but with funding for hospitals falling behind demand for services and payments to doctors expected to grow a third faster than the economy over the next decade. Its new drug program could grow twice as fast. Long term, in the dry language of the 2005 Medicare trustees report, “Growth of this magnitude, if realized, would place a substantially greater strain on the nation’s workers, Medicare beneficiaries and the federal budget.”

Bruce Bartlett, a former executive director of the Joint Economic Committee of Congress who worked in the Reagan White House, put this in perspective recently in the New York Times. To address Medicare’s unfunded liability, he wrote, “We would need to increase taxes by 7.1 percent of GDP immediately and forever just to pay for all the Medicare benefits that have been promised – an amount close to what is now raised by the individual income tax.”

So there’s an interesting problem. Now add 45 million Americans without health coverage, increasingly a result of the implosion of employer-sponsored health coverage, and toss in new technologies in medical care that save lives but cost a bundle. The federal government encourages states to experiment with potential answers to this prelude to a catastrophe and you can see why: Who wouldn’t want to pass it along?

But there is something the federal government could do, something that would give states guidance, and that has been neatly set up by Part D and in the private Medicare Advantage plans. Congress could allow Americans to sign up for Medicare starting at age 55 instead of 65, bringing healthier people into the system, some who could trade their current coverage but also about 3.5 million with no insurance now. And unlike the Medicare drug plan, which both excluded a public plan and subsidized the private ones, it could let the two systems compete fairly on price, quality and choice.

Lowering Medicare’s age limit isn’t a new idea, but it keeps looking better as time passes and the financing problem grows larger. Robert Bixby, executive director of the Concord Coalition, which spends its time trying to persuade Congress to budget responsibly, recently said that to fix Medicare means “to look at solutions that affect the entire health care system.” He was seconded by Robert Greenstein, executive director of the Center on Budget and Policy Priorities, who added that other fixes include premiums for people with higher incomes and maybe a value-added tax to help pay for it.

Those may be necessary, too, but starting at age 55 helps by lowering the per-person cost of care. Spreading risks is the basis of insurance, but it is an idea nearly lost in some of the plans being debated today. Healthy people are being misled into believing that they should pay less than the sick because they cost less to cover. It’s true that they do. For now. But will these healthy people still be healthy in 15 or 20 years? The cost of an individual to the health care system can be accurately measured only at death; the healthy subsidize others in part so that some day someone will be there to subsidize them.

Every day, millions of Americans get effective health care through Medicare, reporting higher rates of satisfaction for the government system, which is not rising in cost nearly as fast as private insurance. Private Medicare plans have been available for years but haven’t been very popular. Part D could change that by making beneficiaries more comfortable with these plans. By lowering the entry age to 55 and controlling for adverse selection, Congress could let beneficiaries decide the question through public-private competition.

Why shouldn’t Congress simply tell states to do what Massachusetts just did and create a mandate for everyone to buy health insurance? Under that plan, businesses with more than 10 employees either provide coverage or get assessed $295 per employee annually. That money along with some income-tax penalties and other subsidies would create a pool to help those who can’t afford the mandate. But without a way to keep costs down, the commonwealth may find that it can’t levy enough funding into its free-pool care. Yet were it to lean on insurers and hospitals to restrict costs, the deal would become much more contentious. I hope Massachusetts works this out, but despite the media applause this week, it would be naive to think these difficulties have been solved.

Medicare, however, isn’t a theory in search of confirmation. Despite its funding problems, it has provided coverage for 40 years, weathering the politics of Washington and the growing demands on it. This isn’t to argue that the system merely needs more money. But the debates over its many benefits vs. the challenges of over-consumption of care, underpayment to doctors and efficiency compared with private plans could be tested even as more Americans received coverage and Medicare itself was put on firmer financial ground.

With that settled, just imagine how much more could be saved if those ages 45-54 could join Medicare too.

Todd Benoit is the editorial page editor of the Bangor Daily News.