President Bush (search), faced with complaints from Republicans as well as Democrats about higher cost estimates for a new Medicare drug benefit, said Friday he would veto any attempt to change the law.

The presidential threat appeared to have little impact on Democrats. They argue that the 2003 Medicare overhaul needs to give seniors more access to affordable prescriptions by permitting drug importation from Canada and allowing the government to negotiate drug prices. Both practices are opposed by Republicans, led by Bush, and forbidden by law.

"This is an attempt by the president to stop the bipartisan groundswell for drug reimportation and price negotiation and just the latest example of the Republican Party putting special interests ahead of the American people," said Senate Minority Leader Harry Reid (search), D-Nev.

Bush raised the matter, without commenting on any specific proposal, as he praised the Medicare law during the swearing-in ceremony for Mike O. Leavitt as secretary of the Department of Health and Human Services (search).

"I signed Medicare reform proudly," Bush said. "And any attempt to limit the choices of our seniors and to take away their prescription drug coverage under Medicare will meet my veto."

Congress narrowly approved the legislation in 2003, which creates coverage for prescription drugs starting in January 2006. After the extraordinary all-night debate, Republican leaders won passage in part by assuring wavering lawmakers that the program's cost would be $400 billion. Just two months later, after the law was enacted, the administration revised the cost estimate to $534 billion.

Earlier this week, the estimate for the first full decade of the program was revised upward again, to $724 billion, mostly because the previous projection had included fewer years when the drug benefit was in effect. That raised questions anew about the White House's credibility and sparked some lawmakers from both sides of the aisle to say the drug benefit should be re-examined.

Some Republicans expressed alarm at the escalating costs, while Democrats said the new figure shows their solutions to drug access are still needed.

White House press secretary Scott McClellan said the president's veto threat was only "a general statement" not tied to any specific legislative idea. But he made clear that it was Democrats that Bush mainly had in mind.

"You've seen some Democrats in recent weeks talking about undermining these reforms," McClellan said. "The president was making very clear to our seniors ... he's not going to let anybody take away what we have provided to you."

Bush pledged this week, after the release of the higher cost projection, to "deal with the unfunded liabilities of Medicare." But he didn't say how he would do that, saying a proposed overhaul of Social Security must be accomplished first.

On Friday, the president portrayed the part of the new Medicare law that provides for a much-larger role for private companies as key steps toward addressing the program's financial problems.

"Seniors will be able to choose a health plan that meets their needs. And health plans will compete for their business, which will lower costs throughout the program," he said.