WASHINGTON – Democrats pushed through legislation Wednesday to add 6 million lower-income children to a popular health insurance program while making deep cuts in federal payments to Medicare HMOs, defying a veto threat from President Bush.

The House voted 225-204, mostly along partisan lines, to pass the legislation, which would add $50 billion to the decade-old State Children’s Health Insurance Program and roll back years of Republican-driven changes to Medicare. Maine Reps. Tom Allen and Mike Michaud, both Democrats, voted for the measure.

It would slash federal payments to private insurance companies that cover seniors under Medicare and shift money to doctors and benefits for low-income seniors.

The legislation sparked a bitterly partisan health care battle on the eve of Congress’ monthlong summer recess.

A raucous debate over the measure – filled with parliamentary fireworks by angry Republicans – engulfed what is otherwise a broadly supported program to insure working poor kids in a larger argument over whether the government or the private sector should provide health insurance to the nation’s most vulnerable populations.

A more limited, $35 billion expansion of the children’s health care program without broader Medicare changes appeared headed for a bipartisan endorsement in the Senate by the end of the week, despite another threatened veto. Bush has proposed spending half as much on the program over the next five years.

In a veto threat of the House bill issued Wednesday, the administration said the legislation “clearly favors government-run health care over private health insurance” and spends far too much.

The decade-old SCHIP program is designed to subsidize the cost of insurance for children whose families earn too much to participate in Medicaid, but not enough to afford private health insurance. Through federal waivers, however, the program has expanded in many states to include middle-income children and adults, prompting Republicans to argue that it has morphed into a backdoor way to extend government-provided health care to an ever-increasing population of Americans.

“This is not just about helping low-income children. This bill today seems to be spending government funds to lure middle class, upper middle class, even wealthy, perhaps, families, to opt out of private health coverage and go to government health coverage,” said Rep. Jim McCrery of Louisiana, the top Republican on the Ways and Means Committee.

Democrats, betting that opposing the measure – which would insure a total of 11 million under SCHIP – would be a political loser for Republicans, painted the GOP opposition as mean-spirited and stingy.

“We are halfway to covering the uninsured children in this country, and the Republicans want to pack up and go home,” said Rep. Diana DeGette, D-Colo.

Beyond health care for children, though, the measure reflected dueling Democratic and Republican health care priorities, especially on how to cover the nation’s seniors, a potent voting bloc. Democrats have long worked to bolster government-provided coverage for seniors under Medicare, while Republicans have favored giving private companies incentives to insure them.

To help pay for the SCHIP increase, Democrats dipped into federal payments to Medicare HMOs, which they argue drive up premiums for seniors in traditional Medicare by inflating the cost of care. Officials estimate the government pays an average of 12 percent more to these private plans than it does for traditional coverage.

Rep. John D. Dingell, D-Mich., chairman of the Energy and Commerce Committee, called the Medicare HMO overpayments “a great injustice,” and said Democrats were determined to “stop that evil practice.”

Republicans said Democrats would live to regret the Medicare cut, which GOP strategists say will prompt angry seniors to exact a steep political price on the majority party.

“Don’t use children as your shield,” said Rep. Mike Rogers, R-Mich. “This is the single largest cut to Medicare in the program’s history.”

The rest of the increase would be financed by a 45-cent-per-pack cigarette tax increase.