WASHINGTON -- President Barack Obama summoned more than a dozen Democrats from the House of Representatives to the White House, pleading with them to put aside their qualms and vote for his massive health care overhaul.

In back-to-back meetings Thursday, Obama urged uneasy rank-and-file moderates and progressives to focus on the positives rather than their deep disappointment with parts of the bill. The lawmakers said Obama assured them the legislation was merely the first step, and he promised to work with them in the future to improve its provisions.

It's the opportunity of a generation, he told them -- and a chance to revive the party's agenda after his rough first year in office.

"The president very pointedly talked about how important this is historically," said Democratic Rep. Raul Grijalva, "how he needs our help." Obama told them that "'this is an opportunity, it'll give us momentum"' on other issues, the congressman said.

Congressional leaders said they were hoping for votes on the legislation in as soon as two or three weeks.

More On This...

White House spokesman Robert Gibbs told reporters he believes the House is on schedule to approve the landmark legislation by March 18, when the president leaves for an Asian trip, and he can sign it into law "shortly thereafter."

Concerned about fellow Democrats' trepidation about a legislative drive that has garnered only modest public support, House leaders expressed optimism but hardly certainty that they would nail down enough support that soon. Democrats have repeatedly missed self-imposed deadlines for moving the legislation.

On Wednesday, Obama made what was expected to be his final push to overhaul the U.S. health care system, announcing a revised plan at the White House in an attempt to win the support of moderate Democrats.

Though Obama's latest proposal included some ideas favored by Republicans, he has little hope of winning over even one member of the conservative party. Republicans want to scrap the plan and start over.

However, the White House hopes that including elements of Republican plans will entice Democratic lawmakers from conservative districts whose re-election hopes in November could be jeopardized by voting for the bill.

Obama's revved-up personal involvement, along with the cautious tone of congressional leaders' forecasts, illustrated the uncertainty still facing the president's yearlong drive to push his signature legislative initiative through Congress.

The United States is the only major industrialized country without a comprehensive health care plan. Nearly 50 million people are uninsured.

Lawmakers were almost finished merging House and Senate versions of sweeping health care overhaul legislation when a special election in January cost Democrats a key Senate seat. The Senate Democrats were left one seat shy of the margin they needed to bypass Republican stalling tactics, throwing the reform effort into disarray.

Under the current strategy, Democratic leaders want Congress to send Obama the nearly $1 trillion health overhaul that the Senate passed in December, plus a separate bill making changes that House Democrats want.

Of the House Democrats Obama met with on Thursday, all but two voted for a more far-reaching version of the health bill last year. The attendance list spotlighted the White House's need to reassure those supporters on the legislation, even as it struggles to retain backing from more moderate Democrats worried about the bill's costs and its language on abortion.

Republicans say the legislation would create government-controlled health care that the public does not want.

In another event at the White House, Health and Human Services Secretary Kathleen Sebelius met with the chiefs of four major health insurance companies and asked them to provide justifications for double-digit price increases that have angered consumers. Health insurers, who have blamed rising medical costs for their own price rises, made no final commitments about what they would provide.