The promise of a prescription drug benefit should delight the 35 million senior citizens on Medicare. Drugs are the biggest out-of-pocket expense for many enrolled in the federal insurance plan. But before popping the celebratory cork, take a long, sober look at the details of the complicated plans wending their way through Congress this month. Whatever reform is enacted could take a long while to take effect, and what's more, it might open as many gaps as it closes.

Elderly people on Medicare are expected to spend $1.8 trillion on drugs in the decade beginning 2004. The congressional plans--both the Senate and the House are crafting bills--would cover about $400 billion of that cost. The current political debate centers on how to spend that money, and on whom. For example, some want the new money to favor the typical prescription drug consumer, while others want the money to favor those with sky-high costs. In either case, elderly people are going to end up with significant prescription drug bills.

And the drug benefit only comes with trade-offs. The House version, for example, calls for new copayments for home health aides. The Senate bill would require new copayments for routine laboratory tests, and perhaps greater copays for medical equipment such as wheelchairs. All of that amounts to additional out-of-pocket costs for patients. A cost-benefit analysis of each plan for each individual is so complicated, says Vicki Gottlich, attorney with the Center for Medicare Advocacy, that those over 65 "are going to have to be mathematicians and seers."

Perhaps most distressing to senior citizens groups is the looming loss of parity. For 38 years, Medicare has provided equal benefits to everyone over 65, regardless of income. That would no longer be the case. The Senate bill would not provide a drug benefit to the lowest- income seniors. Instead, those people would get drugs through Medicaid, the state programs for the poor, which vary considerably from state to state. And those opting for private plans would get benefits different from those offered to people who stay with the traditional Medicare fee-for-service plan.

Stability. The reformed Medicare could also be less predictable for seniors. "Medicare has always been a guaranteed stable benefit. You always knew what your out-of-pocket expenses would be," says Gottlich. Experiments with Medicare HMOs--called Medicare-plus-Choice--resulted in benefit packages and premiums that changed from year to year, and studies show that senior citizens like the existing system for its predictability. Indeed, a survey by the Commonwealth Fund found that 62 percent of Medicare beneficiaries are very satisfied with their healthcare, compared with only 51 percent of younger people covered by private insurance plans.

Despite all the political pressure to get a prescription drug benefit into Medicare, senior citizens groups are wary about the details. For example, the influential AARP is withholding its thumbs up or thumbs down on the current bills. One of the biggest concerns, says John Rother, the group's policy director, is what is being called the "doughnut hole." The House and Senate versions of the plan have various deductibles, premiums, and copayments for drugs, but both plans would create gaps in coverage: In the House plan, there would be no coverage for drug costs between $2,000 and $5,100; in the Senate plan, coverage would stop between $4,500 and $5,800 before kicking in again.

And that's what seniors just don't get. "The one that hits our members the hardest is the idea of a benefit gap, or doughnut hole, in the middle," says Rother. "People don't understand why Congress would design something that eliminates coverage just when your need gets serious." It is, of course, a cost-saving measure. Seniors would bear those costs in the middle, while still being protected from catastrophic costs as their bills rise.

The overall goal, says Secretary of Health and Human Services Tommy Thompson, is to revitalize Medicare and give people a choice of insurance plans. His department will have 2 1/2 years to explain whatever plan emerges to the people who need it. "We will be spending millions of dollars on advertising to explain this to the seniors. We'll advertise on television, in magazines. We'll send out brochures giving them their options in region-specific areas," says Thompson, adding: "Everybody will know what he or she is entitled to."