Washington ? In a triumph for President Barack Obama, Democrats narrowly pushed sweeping health care legislation through a key congressional committee Friday night and cleared the way for a September showdown in the House.

The 31-28 vote in the House Energy and Commerce Committee, along party lines, was weeks later than either the White House or Democratic leaders had hoped.

As part of a last-minute series of changes, the committee agreed to cap increases in the cost of insurance sold under the bill, and also to give the federal government authority to negotiate directly with drug companies for lower prices under Medicare.

The new provisions were part of an intensive effort Democrats made in recent days to satisfy the conflicting demands of liberals and conservatives on the panel, unity necessary to overcome a solid wall of Republican opposition.

“We have agreed we need to pull together,” said Rep. Henry Waxman, D-Calif., the committee chairman who presided over hours of private negotiations and public committee meetings. Five Democrats opposed the bill.

The measure is designed to extend health insurance to millions who now lack it, at the same time it strives to slow the growth in medical costs nationwide — Obama’s twin goals.

While the pace of action was slower than party leaders had hoped, it was speedier by far than the timetable in the Senate.

There, Democrats said a deadline of Sept. 15 had been imposed on marathon talks aimed at producing a bipartisan compromise. Several officials said Sen. Max Baucus, D-Mont., had informed fellow senators he intends to convene his Finance Committee to begin voting by then.

Without a bipartisan bill, Baucus would presumably have to produce a measure tailored to Democratic specifications, a step he has said repeatedly he would rather avoid. It wasn’t clear how much the deadline was Baucus’ idea, and how much it reflected growing impatience at the White House and on the part of Senate Majority Leader Harry Reid of Nevada.

The Energy and Commerce Committee was the third of three House panels to act on the legislation, a measure that numerous lawmakers note would rearrange one-sixth of the nation’s economy. A vote in the full House is expected in September, after lawmakers return from a monthlong vacation.

In the run-up to final approval, the panel handed the drug industry a victory, voting 47-11 to grant 12 years of market protection to high-tech drugs used to combat cancer, Parkinson’s and other deadly diseases. The decision was a setback for the White House, which had hoped to give patients faster access to generic versions of costly biotech medicines like the blockbuster cancer drug Avastin.

Democrats also turned back a Republican bid to strip out a provision allowing the government to sell insurance in competition with private industry. The vote was 31-28, reflecting the shaky majority Democrats had on a 59-member committee they nominally controlled with 36 members.

Under the bill, insurance companies would be required to sell coverage to all seeking it, without exclusions for pre-existing medical conditions. The federal government would provide subsidies for lower-income families to help them afford policies that would otherwise be out of their reach.

The bills would set up so-called exchanges, in effect national marketplaces where consumers both with and without subsidies could evaluate different policies and choose the one they wanted.

The main expansion of coverage would not come until 2013 — after the next presidential election.