IT'S HARD to believe, but Medicare's open-enrollment season ends today. And this year, as a result of the federal health-reform law, seniors who rely on privately administered Medicare Advantage plans for their benefits will face some big adjustments.

Under the Medicare Advantage (M.A.) program, private insurers offer competing Part A Hospital and Part B Physician Care plans, and patients themselves choose which coverage option works best for their health and financial needs. M.A. insurers must provide at least the same benefits as traditional Medicare, but most offer more. The government reimburses insurers at a preset rate per enrollee.

More than 12 million seniors participate in Medicare Advantage, about one-fourth of all those eligible for Medicare. The program has grown popular thanks largely to its competitive structure, which encourages insurers to vie with one another for seniors' health-care dollars.

But some policymakers believe the M.A. program to be wasteful. They cite the fact that Medicare Advantage costs the government slightly more per enrollee than traditional Medicare. They believe that seniors would be better served if everyone was enrolled in the traditional Medicare program.

This contention also ignores the reality that most people in traditional Medicare buy supplemental coverage if they can afford it. Medicare Advantage provides millions of seniors with extra health-plan services at an affordable price - services they would not have access to if their only affordable choice was traditional Medicare.

Unfortunately, the new health-reform law includes a provision designed to eliminate choice and push more seniors into traditional Medicare coverage. The new law changes the special Medicare Advantage open-enrollment period that occurs each year in January.

Previously, Medicare beneficiaries were allowed to either change from one Medicare Advantage plan to another, or to change from Medicare Advantage to traditional fee-for-service Medicare. Beginning in January, seniors will be allowed only to opt out of the Medicare Advantage plan they chose in 2011 to enroll in traditional fee-for-service Medicare.

Moreover, this year the health-reform law froze Medicare Advantage payment rates to participating insurers at 2010 levels - that is, it didn't allow reimbursements to be adjusted for inflation. Next year, payments will be cut further. By 2017, government number-crunchers expect benefits for the average M.A enrollee to be slashed by 27 percent, or $3,700.

The Congressional Budget Office (CBO) estimates that these changes will cause some Medicare Advantage plans to exit the program and that, as a result, enrollment will drop to 7.4 million by 2017. The Medicare program's own actuaries predict an even steeper fall-off of 50 percent.

That's a shame, as Medicare Advantage delivers more benefits - and superior outcomes - than traditional Medicare. According to the CBO, individual patients enjoy many value-added services that help them maintain their health and well-being, such as lower co-pays, premium rebates, and coverage or deep discounts for services like dental work and eyeglasses. And a 2004 study found that M.A. plans achieved better outcomes than traditional Medicare in five of seven core indicators, including breast-cancer screenings, diabetes-testing and treatment after heart attacks.

Medicare Advantage represents just the kind of innovative health-care model that could help drive down long-term health costs and improve health care in this country. Congress should make it easier to opt in, not out. And if seniors want to change plans, they should have a full range of choices available to them.