President Bush said Wednesday Medicare is next on the government’s fix-it list because the health care plan for the elderly and disabled, like Social Security, is facing financial stress with the retirements of baby boomers.

Administration officials said earlier that the new Medicare prescription drug benefit will cost taxpayers $720 billion over its first full 10 years, a far higher estimate than the $400 billion the administration promised lawmakers when Congress narrowly approved Medicare legislation in 2003. The estimate also exceeds the revised estimate of $534 billion that the White House issued just two months later, after the law was enacted.

“There’s no question that there is an unfunded liability inherent in Medicare that Congress and the administration is going to have to deal with over time,” Bush said. “Obviously I’ve chosen to deal with Social Security first and once we accomplish _ once we modernize and save Social Security for a young generation of Americans, then it’ll be time to deal with the unfunded liabilities of Medicare.”

Bush noted that the prescription benefit that he signed into law last year doesn’t take effect until next year.

“I’m convinced they’ll have cost savings for our society,” Bush told reporters during a meeting with Polish President Aleksander Kwasniewski. “And I know it’ll make the life of our seniors better.”

The original estimates for the drug plan ran from 2004 to 2013 _ two years to ramp up the program and then eight years in which the government will pay some drug costs for Medicare beneficiaries. The new projections cover 2006 to 2015, the first decade in which the drug coverage will be operational the entire period.

The drug benefit begins in January and the $720 billion includes the years 2014 and 2015, Medicare spokesman Gary Karr said.

“Of course the costs go up when you add in more years at the end and more people are on Medicare,” Karr said. Drug costs, which have been rising far faster than inflation, also are expected to be higher in those years.

White House budget chief Joshua Bolten said Wednesday the new price tag reflects $134 billion in savings the government expects over the period because states are paying some drug costs; $145 billion more from beneficiaries’ premiums; and $200 billion in savings the program will create for Medicaid.

Added to the $720 billion price tag the administration is using, that would bring the drug program’s gross 10-year cost to $1.2 trillion before the savings.

The $400 billion and $534 billion figures used earlier included the effects of projected savings and are comparable to the $720 billion estimate.

Bolten told the Senate Budget Committee that other than the different decade now being measured, the White House’s cost estimates are “completely consistent with the numbers the administration has produced before.”

Sen. Judd Gregg, R-N.H., the new budget panel chairman and a long-time critic of its costs, said the new numbers did not diminish his concern.

“I do think we are going to have to go back and re-address it,” he told Bolten.

Based on the numbers released Tuesday, the program’s costs are estimated at roughly $100 billion annually in 2014 and 2015, or more than a third of what the Medicare bill was projected to cost in its first 10 years.

Under the new program, participants will pay monthly premiums that are expected to average $35 in 2006 and the first $250 in drug costs. Medicare will pick up 75 percent of the next $2,000 in prescription expenses. After that, a gap is built into coverage during which participants are responsible for the entire drug bills until costs top $5,100, after which the government pays 95 percent.

Controversy over cost has plagued the program since before its passage. The administration’s Medicare chief pressured a subordinate to withhold his higher estimates of the cost of the legislation from Congress, a report by the Department of Health and Human Services inspector general concluded.

The issue was politically significant because several Republicans in the House stated before final congressional approval of the legislation that they would not support a bill that cost more than $400 billion. The bill narrowly passed the House, 220-215, after an extraordinary three-hour, middle-of-the-night vote in which GOP leaders and administration officials cajoled reluctant Republicans to support President Bush’s key domestic priority.

Conservative Republicans have expressed concern about Medicare costs, while Democrats have accused the administration of hiding the law’s true costs.