The costs of the Medicare and Medicaid health insurance programs are rising at unsustainable rates that will force policy makers to adopt major changes to curb spending, the head of the Congressional Budget Office warned on Monday.

The two programs for the poor, elderly and disabled now consume 4 percent of U.S. gross domestic product, a figure that could rise to 20 percent in 50 years if current patterns continue, CBO Director Douglas Holtz-Eakin said.

“The growth of these programs is simply unsustainable. Big changes are coming regardless of what you might think at the moment,” he told the World Health Care Congress, a meeting of 1,400 health industry executives.

States and the federal government share Medicaid costs, while the federal government alone funds Medicare. Federal spending on the programs makes them the third largest part of the federal budget, behind only defense and Social Security.

Holtz-Eakin forecast Medicare and Medicaid would cost taxpayers more than Social Security within 10 years, when those three programs combined would account for more than half of all federal spending.

Twenty percent of Medicare spending a decade from now likely will go toward new prescription drug benefits that take effect in 2006, Holtz-Eakin said.

He and other experts said there are no “silver bullets” to reduce costs.

“There is not a single item - technology, disease management and tort law reform - that is the answer. It’s more likely we will have a series of incremental changes that will spell the future of our health care system,” he said.

Gail Wilensky, a health care analyst and former head of Medicare and Medicaid, said lawmakers “lost an opportunity” to lower costs when they added the drug benefit in late 2003.

“It’s a good example of eating dessert first,” she said.

Mark McClellan, administrator of the Centers for Medicare and Medicaid Services, said the agency already was taking numerous steps to bring costs down. He announced a new pilot program to give doctors financial incentives to cut costs and produce better health outcomes for Medicare beneficiaries. Ten of the nation’s largest physician practices, which provide care to thousands of Medicare patients, will participate in the three-year test, he said.

“I think it can save us significant amounts of money,” McClellan said.

Wilensky said the various changes touted by McClellan were “frankly kind of baby steps.”