With a new nudge from President Bush, congressional negotiators labored Wednesday to reach agreement on legislation to provide the elderly with a prescription drug benefit under Medicare (search).

Bush brought senior citizens, interest groups and others hoping for a bill to the White House for a round-table discussion and pep rally. He also brought up the issue during an Oval Office breakfast with Republican and Democratic leaders of Congress.

"I urge the Congress to act quickly, to act this year, not to push this responsibility to the future," the president told his White House audience. "We have the opportunity, we have the obligation to give seniors more choices and better benefits."

As Bush spoke, Republicans worried that the bill they were writing could exceed the $400 billion limit set by the president -- an idea the president's spokesman firmly rejected.

"That was what was agreed to," White House press secretary Scott McClellan said. "That's a historic increase in funding for Medicare."

Each house passed a version of the complex legislation in June.

Lawmakers trying to hammer out a compromise version have reached tentative agreement in several areas, but still under discussion are controversial topics such as higher premiums for wealthier seniors. The negotiators remain further apart on a few thornier issues, such as the calls for direct competition between traditional Medicare and private health plans; limits on spending if future cost increases are larger than expected; and tax-preferred savings accounts (search) that people could use to meet their medical costs.

With the White House eager for a bill Bush can tout on the campaign trail -- and with time running out as Congress looks toward a pre-Thanksgiving adjournment for the year -- McClellan would not reveal the president's stance on many of those provisions or even confirm that Bush has communicated his preferences to the negotiators.

"The president has outlined a framework and he's been working closely with members of Congress to get this passed," McClellan said.

Bush himself talked only broadly of the benefits of a Medicare bill. Despite worries among some elderly people about whether the bill would actually provide noticeable help for their widely varying expenses, the president said those with no prescription coverage now would "see their drug bills cut roughly in half" and that the Great Society (search)-era program would see cost savings as the use of drugs to prevent health conditions eliminates the need to pay for their costly treatment later.

But representatives of consumer, labor and liberal interest groups criticized the proposed drug benefit as insufficient and too complicated. They called the bill a thinly veiled effort to undermine traditional Medicare and replace it with private insurance.

"We said we'd support a bill that is not all we want as long as it is a sound design," said Gerald Shea, an AFL-CIO (search) official. "This is going to be a disaster, we fear, for retirees."

Democratic presidential candidate Joe Lieberman said Bush must press Republican lawmakers "to stop the push for privatization under the deceptive mantra of modernization."