THE PROGRAM NOW consumes one-eighth of the federal budget; in 10 years that share is expected to grow to one-fifth. It will consume more money this year than enters the Treasury through payroll taxes. By 2019, if current spending patterns hold, the trust fund that finances the biggest part of the program will be out of cash.

The program is not Social Security but Medicare. Those frightening figures emerged during what might be called the Medicare Moment of President Bush's economic summit -- an official pause to recognize the problem and then crisply move on. "My role is to say: 'Remember health care, remember Medicare,' " said Dr. William Roper, dean of the University of North Carolina School of Medicine. Indeed, the figures tell the story. Medicare is a bigger problem than Social Security: its hospital care trust fund is on track to go bust two or even three decades before the Social Security surplus runs out; its unfunded liabilities dwarf those of Social Security -- $27.7 trillion over the next 75 years, compared with $3.7 trillion liability for Social Security.

So why is the administration devoting its attention to Social Security rather than grappling with the bigger problem? One answer may be that, as ambitious as the administration's plans for private accounts may be, "fixing" Social Security is by far the easier task. Medicare faces the same relentless demographic pressures as Social Security -- plus the burden of rapidly rising health care costs. Another may be that grappling with Medicare will require thinking about the nation's irrational health care system as a whole, a task for which the administration and Congress appear to have little stomach.

Indeed, the gaping Medicare hole was dug even deeper last year with the adoption of a new prescription drug plan for seniors. The administration initially sought to link moves to constrain Medicare costs with the prescription drug benefit, but the legislation ended up with a supersized new benefit and slimmed-down cost-containment measures that mostly take effect -- if they work -- years down the road. The Government Accountability Office estimated earlier this month that the drug benefit will cost $8.1 trillion over the next 75 years -- and that's if politicians resist the temptation to fill in the "doughnut hole" gap in coverage. Comptroller General David M. Walker called the drug plan "one of the largest unfunded liabilities ever undertaken by the U.S. government."

You wouldn't know it from Mr. Bush, though, and that's the truly scary part as he presses for Social Security reform. "We did take on Medicare, and it was the Medicare reform bill that really began to change Medicare as we knew it," he said at his news conference Dec. 20. "It introduced market forces for the first time, provided a prescription drug coverage for our seniors, which I believe will be cost-effective. I recognize some of the actuaries haven't come to that conclusion yet, but the logic is irrefutable."

Actually, none of the actuaries have come to that conclusion; their only disagreement is about how mammoth the cost will be. And while the president is right that in some cases paying for prescription medication saves money down the road, we disagree in suggesting that the drug benefit will even come close to paying for itself overall. Mr. Bush's rosy scenario notwithstanding, Dr. Roper's admonition -- "remember Medicare" -- is precisely on point.

Commentary: