Updated

President Bush said Saturday that Congress must deliver on prescription drugs for Medicare, a promise made by Bush and congressional candidates across the country.

"Medicare is an essential program, but it has not kept pace with the advances in medicine," Bush said in his weekly radio address. "We need to do more to fulfill Medicare's promise."

It was the second day running that Bush pressed for changes in Medicare, the health insurance program serving 40 million elderly and disabled Americans.

Democrats and Republicans in Congress are working to shape a prescription drug plan. There are significant disagreements over how much to spend, how generous the benefit should be and how to structure the coverage.

At the same time, lobbyists for hospitals, doctors, health maintenance organizations and other health care providers are fighting over limited dollars available for Medicare payments.

Unlike most private health plans, Medicare does not cover prescription drugs administered outside the hospital — which dates back to 1965, when Medicare was created.

Some seniors buy private drug coverage and others sign up for health maintenance organizations and other managed care plans offered through Medicare, which generally offer prescription drugs. Still, nearly one in three Medicare beneficiaries has no drug coverage at all.

That has to change, Bush said Saturday.

"Seniors often pay the highest prices for drugs out of their own pockets, forcing too many of our seniors to choose between paying for pills or paying their bills," he said.

Bush made the same point during his run for president, as did scores of congressional candidates. Medicare drug coverage was the most popular topic in TV ads in 2000, and everyone was for it.

Democrats hold a solid advantage on the issue, but GOP strategists believe that passing a drug bill this year would blunt their arguments in fall campaigns.

Making it happen isn't easy.

Lawmakers are proposing more spending for Medicare than the $190 billion over 10 years that Bush put into his budget. In the House, Republicans have a $350 billion, 10-year plan. In the Senate, a pair of Democrats have a plan estimated at $450 billion to $500 billion, though it doesn't include 10 full years.

Whatever the final number, it will have to pay for the costly new drug benefit as well as any payment increases to health care providers.

The president wants more for HMOs, which take a set fee for each Medicare beneficiary who signs up and then cover all medical costs. HMOs complain that they don't get enough and more than 100 plans have dropped out of the Medicare program.

Ultimately, many Republicans want Medicare to function much like its HMO division — with seniors picking among private plans for their health coverage.

At one time, Republicans were insisting on tying any new drug benefit to a wholesale restructuring of the program that encourages this sort of competition.

Today, Republican goals for involving private companies are more modest. They want private insurers to administer the drug plan, following guidelines set by government.

Democrats say drug coverage should be part of the central program.

Other differences involve how much to spend, which determines how much seniors will have to pay for each prescription and how much they will have to spend before government begins paying the full cost.

With these differences separating the parties, it's doubtful Congress will pass a bill this year, said Ronald Pollack, president of Families USA, a liberal consumer group.

"Maybe there's a glimmer of a possibility," he said.

Others say the political pressure will force the parties to work out their differences.

"Are they going to be satisfied with going back and saying, 'Trust me one more time?"' Health and Human Services Secretary Tommy Thompson said recently. "Come August, September, the pressure is going to be very high to deliver on prescription drugs."