Divided along ideological as well as political lines, senior lawmakers from the House and Senate pledged their best efforts to find common ground Tuesday as they opened talks over Medicare (search) prescription drug and modernization legislation.

"This is not going to be easy," said Rep. W.J. Tauzin (search), R-La., chairman of the House Energy Committee, a prediction that drew no dissent.

"Some say the bills go too far. Some say not far enough," said Sen. Charles Grassley (search), R-Iowa, chairman of the Senate Finance Committee. "Policy differences are fine. But lines in the sand are not."

The meeting consisted of little more than gentle jockeying for position, and no policy differences were debated nor deadlines set for agreement on legislation that several lawmakers said marked a historic opportunity.

The hard work of compromise will begin in the coming days, as lawmakers try to mesh different bills passed by the House and Senate, each designed to achieve twin objectives.

Both bills would provide prescription drug benefits for older people, delivered through private insurance companies and subsidized by the government.

In addition, the measures would inject greater competition into the 38-year-old Medicare program by creating an expanded role for managed-care companies. The Bush administration and Republicans say such changes are needed to shore up Medicare's finances while producing a more modern program at the same time that would also improve Medicare's financial outlook.

The two bills vary greatly, differences reflected in the outcome of voting on the floors of the House and Senate. The House bill, drafted by GOP leaders to appeal to conservatives, cleared by a one-vote margin with only nine Democrats in support. The Senate bill, by contrast, passed overwhelmingly with bipartisan backing, as reflected in support by both Majority Leader Bill Frist, R-Tenn., and Democratic leader Tom Daschle of South Dakota.

The key disputes are likely to center on a provision in the House bill that would force traditional Medicare to compete with private plans beginning in 2010. Conservatives argue that is key to incorporating changes in Medicare needed to ensure its financial stability. Democrats argue it's a prescription for the disintegration of a four-decade-old program, with ever-escalating premiums for seniors who remain in the existing programs.

For their part, Senate Democrats want the final measure to assure that the government would step in to offer a prescription drug benefit if private industry failed to do so in any of the regions set up for the program. Republicans argue against that, saying it would reduce the likelihood of private involvement.

Apart from policy differences, Medicare is a politically charged as well, particularly in the House.

The House Democratic campaign committee has been airing commercials in eight congressional districts in recent days quoting a House Republican as bragging he wants to "end Medicare as we know it." The commercials accuse each of the eight lawmakers of casting the deciding vote on legislation that would do that, a bill that "pushes seniors into HMOs and insurance companies."

Kori Bernards, a spokeswoman for the Democrats, would not say how much was spent on the ads. "It's enough to be felt and heard in these districts by these members who are already very vulnerable on this issue," she said.

Republicans argued otherwise. "Democrats are spending money they don't have on an issue they can't win. They're trying to keep this from being a feather in our cap," said Carl Forti, a spokesman for the GOP campaign committee.

Political campaign commercials generally are not aired until much closer to election day. GOP congressional aides put the cost of the Democratic ads at less than $200,000 in the eight districts combined and said the average targeted viewer would see the ad only once or twice, far fewer times than average end-of-campaign level of advertising.

At the same time, Democrats worked aggressively to encourage local television stations to report on the commercials in the eight congressional districts, seeking to expand the number of viewers with a technique both parties sometimes employ.