The legislation would launch the most significant growth in federal health care in a decade, and Democrats hope it will fortify their members as they head home soon for the summer recess amid voter perceptions that they have accomplished little since taking control of Congress.

"This is the children's hour," House Speaker Nancy Pelosi (D-Calif.) declared last night. "We are able to meet our moral obligation to our children."

The 225 to 204 vote in the House — largely along party lines — came after hours of delaying tactics, strident rhetoric and trench warfare from Republicans who called the bill the first step toward "socialized medicine," financed by an unfair tobacco tax increase and cuts to managed-care companies in Medicare.

But in the end, the Democrats had weapons that were just too powerful — a promise to insure 5 million more children who otherwise would have no access to health care, adding to the 6 million children already covered — and the backing of Republican and Democratic governors, the American Medical Association, AARP, the March of Dimes, the Catholic Health Association, the American Academy of Pediatrics, and even cyclist Lance Armstrong. And the prospects are good in the Senate, where a key Republican, Orrin Hatch (Utah), said, "It's difficult for me to understand how anyone wouldn't want to do this."

But Bush opposes such a major expansion of the program. In an interview with The Washington Post last month, he said, "When you expand eligibility . . . you're really beginning to open up an avenue for people to switch from private insurance to the government."

The House bill would enlarge the State Children's Health Insurance Program, or SCHIP, by $47 billion over five years to provide coverage to the additional 5 million children.

Those children would have access to dental and mental health care. And the bill would offer new options for states to extend Medicaid and SCHIP coverage up to age 20 and to cover some legal immigrants and pregnant women. It would expand coverage for preventive health screening for seniors under Medicare and would provide $19 billion over five years to prevent scheduled cuts to physician reimbursements under Medicare. Nearly $3 billion is included for rural health care.

To pay for it, the bill would raise the federal tobacco tax by 45 cents a pack, while making federal payments to managed-care plans under Medicare equal to reimbursements for the federally managed Medicare program.

The bill, which last month appeared to be politically unassailable, stirred a pitched battle on the House floor. Democrats charged that Republicans were fighting to deny health care to children, using scare tactics and false charges to mask their true intentions. Republicans accused Democrats of pushing nationalized health care while accusing them of slashing Medicare and imperiling seniors.

"Folks, that's the bottom line: It's government-paid health care," Rep. J. Dennis Hastert (R-Ill.) said in a rare speech since he lost the House speakership in the Democratic takeover. "It's a bad bill for a bad time, and it's coming under the false pretenses of trying to do something for children."

House Minority Leader John A. Boehner (Ohio), pointing to the cuts to Medicare managed-care plans, dashed off a letter to AARP, calling for the powerful seniors lobby to retract its endorsement and halt its full-throttle campaign for its passage.

But John Rother, AARP's policy director, responded that funding for Medicare physician reimbursements and free medical screenings more than makes up for any difficulties managed-care companies might face when they reap the same reimbursement rates as the core Medicare program.

The Senate measure, a $35 billion expansion of the program over five years, would continue coverage for about 1 million children who might otherwise be dropped and add an additional 3 million youngsters.

By forgoing the physician reimbursement issue and rural health-care funding, senators could pay for it with a 61-cent increase in the federal tobacco tax while avoiding any Medicare cuts. That has given the Senate bill broad, bipartisan support, but House Democratic leaders say the advocacy of Hatch and several other conservatives will give their members ample political cover when negotiators try to reconcile the House and Senate versions.

Hatch and Sen. Edward M. Kennedy (D-Mass.) said yesterday that House-Senate negotiations would aim to keep the final measure to the scope of the Senate bill, in hopes of avoiding a veto.

"Personally, I believe if we can get enough votes, the president doesn't want to veto this," Hatch said.

House Republican leaders believe they have turned the issue against the Democrats. Earlier this week, Rahm Emanuel (D-Ill.), the House Democratic Caucus chairman, huddled with his caucus behind closed doors to soothe frayed nerves. His tool was an advertisement that Rep. Chet Edwards (D-Tex.) depended on to gain reelection in 2004, when an unprecedented redistricting in his state had made his electorate strongly Republican.

"I don't want welfare. I just want to get insurance for my child," Jenny Jones, 28, said in the advertisement, after explaining that her husband had been killed two years before in a house fire, leaving her 3-year-old daughter, Bailey, dependent on the Children's Health Insurance Program. "Look at my little girl, look into her eyes and tell her she's not good enough to be taken care of."