Washington ? Legislation to remake Medicare advanced in the House and Senate early today as key lawmakers struggled to pass bills offering prescription drug coverage to seniors while giving private insurance companies a broad new role in the program.

The Senate’s march toward passage hit an unexpected roadblock at midnight, when a provision to charge affluent seniors higher premiums for doctor and nonhospital services under traditional Medicare survived a test vote, 59-38.

Sen. Edward M. Kennedy, D-Mass., who has played a critical role in supporting the bipartisan legislation, sought to block formal adoption of the proposal, but its supporters insisted it go into the bill. The result was a lengthy delay in which a knot of senators animatedly debated their next move informally in the well of the Senate.

Across the Capitol, House Republicans lobbied hour after hour in their effort to lock up enough votes to assure passage of a more partisan measure. GOP aides expressed confidence they would prevail, yet conceded the outcome was likely to be far closer than they had anticipated.

There was little hint of the difficulties earlier in the day, as both houses embarked on a debate of historic proportions.

“Today we will take the first steps in creating the next generation of health care,” said Rep. Deborah Pryce, R-Ohio.

The House debate was sharply partisan as Democrats attacked a GOP-crafted bill as an attempt to privatize Medicare and donned black armbands as if mourning the program’s demise. “It’s a sham,” charged Rep. Fortney Stark, D-Calif.

“I find it amazing that they go back to the same old scare statements,” retorted Rep. Bill Thomas, a California Republican and key architect of the bill that combined the drug benefit with a new managed care option that seniors could select instead of traditional Medicare.

The Senate proceedings were more collegial, punctuated by a 71-26 vote to divide the bill’s remaining $12 billion evenly between priorities favored by Republicans and Democrats.