Washington ? It did not take President Bush long to begin capitalizing on his push in Congress to reform Medicare and add a prescription drug benefit for seniors. Three days after the House and Senate passed their separate Medicare bills, he was in Miami talking about the “historic opportunity we have to modernize Medicare on behalf of America’s seniors.”

It might happen. But, just as the president’s “mission accomplished” speech on the deck of the Abraham Lincoln last May 1 now seems a premature declaration of success in Iraq, he may be minimizing both the political and policy obstacles to a Medicare victory worth celebrating.

The House and Senate bills have “a lot of commonality,” Bush told the Miami audience, adding that he was confident that House-Senate conferees will “iron out the differences in a constructive way and get a good bill to my desk.” They may, but it is uncertain how well their product will be received.

Failure to finish the legislation, say both Republican and Democratic consultants, would entail huge political risks for any incumbent running next year in a competitive district or state. As Bill Novelli, the head of AARP, the largest senior citizens group, told me, “Virtually every candidate has essentially promised to get drug coverage. The voters would not take kindly” to their coming back empty-handed.

That political imperative is the best reason to think Bush will be able to have a bill-signing ceremony. But hammering out a final version of this complex legislation will be arduous, and the conferees have little room to maneuver. The House version passed by a single vote over almost-solid Democratic opposition — and only after Republican leaders held the roll call open for an hour while they bargained with three of their reluctant members. The Senate had a much wider majority, but the Democrats who were key to making that bipartisan victory possible — Ted Kennedy and Max Baucus, for example — have bottom-line requirements opposed by the main Republican House sponsors.

“The bills are being attacked from the right and the left,” said Novelli. “Conservatives are saying their leadership is giving away the store; this is not real reform. On the left, they’re saying this is the unraveling of Medicare.”

The most contentious issue for the conferees may well be the role of private insurers. House Republicans want to move seniors from Medicare into private plans. They propose heavy subsidies to lure insurers into a marketplace whose costs seem risky to many actuaries. Key Senate Democrats are prepared to fight — perhaps even to filibuster — provisions that go much further than the modest incentives to insurers in the Senate bill.

But there are also important differences in the basic benefits package — especially for lower-income seniors. Estimates collected by The Washington Post illustrate the range. Someone with a drug bill of $3,659 and annual income below the poverty line of $8,980 per year would pay only $91 under the Senate bill, but $1,177 under the House version. Further up the scale, at $14,368 annual income, the Senate bill would leave the retiree with $831 to pay; the House, $2,679. Those are big differences.

Some, including Novelli, worry that seniors may turn against the proposals even before Congress has finished its work. The first poll AARP ran after House and Senate passage showed “the public is pretty confused” about the measures. “The media coverage has been relatively negative,” Novelli said, “so my guess is public opinion will begin to solidify on the negative side. We’re hoping people keep an open mind.”

Robert Blendon of Harvard, who polls on health care politics, said he expects that by 2006, when both bills would begin drug benefits, “it will become very clear” to seniors that “this is inadequate.” If that realization sets in before next year’s election, Blendon said, it may cause problems for members of Congress. “But,” he added, “I think the president will get a lot of benefit in ’04, if he can just get something done. The frustration with Washington doing nothing about the problem is so strong that I think he is pretty immune from any backlash.”

That is also the view of Robert Teeter, the Michigan pollster who ran the elder George Bush’s 1992 campaign. “Health care is one of those issues that is big and complex and difficult,” he said. “Voters are scared to death of giant reforms like this one. But each year, the lack of action is getting to be a worse problem” for the party in power. “And there’s a strong feeling now that nobody can go home next year without having addressed it.”

Getting something done will be difficult — but perhaps it’s manageable. Selling it to seniors could be even tougher.