Democratic efforts to pass the biggest expansion of health care coverage in a decade will set up a titanic political and ideological clash on the floor in both chambers this week.

Democrats are confident the overwhelming popularity of insuring millions of poor children will redound to their political favor — and give them an easily explained accomplishment to tout over the August recess — while Republicans, particularly in the Senate, have struggled to coalesce around an alternative.

The bills to reauthorize and expand the State Children’s Health Insurance Program likely will see significant majorities in both chambers, although Republicans remain confident they will be able to sustain a threatened presidential veto.

The administration and Republican leaders argue the plans would result in the government taking over an ever-larger chunk of the health care system, which they say inevitably will lead to rising taxes and socialized health care.

But House Democrats say moderate Republicans face a stark choice: stand with tobacco companies and insurance companies making obscene profits, or stand with kids, doctors and seniors.

“Do you want to go home and explain to your constituents why you voted to end the children’s health insurance program?” asked Rep. Pete Stark (D-Calif.). Stark questioned the Republicans who are voting “no” this time around. “Ten years ago every Republican member of the Ways and Means Committee voted for SCHIP and a tobacco tax. Now what’s changed? Do they think children are still important?”

The far more ambitious House package, which was still being tweaked late Friday, also whacks subsidies for privately run Medicare Advantage programs to prevent a scheduled cut in pay for doctors and to bolster rural and preventive health care.

House Democratic Caucus Chairman Rahm Emanuel (Ill.) said the package would be an easy sell for Democrats. He noted that millions of children will get health care “and you are going to get fee-free checkups for seniors,” he said.

Rep. Chris Van Hollen (Md.), chairman of the Democratic Congressional Campaign Committee, said the SCHIP package would be a major winner for Democrats.

“You’ve got the Republicans on the side of tobacco companies and those insurance companies that made out like bandits with excessive Medicare subsidies,” Van Hollen said.

House Republicans are finding it a bit easier to unify on ideological grounds than their Senate counterparts, arguing that the government shouldn’t be taking over health care.

Rep. Tom Price (R-Ga.) has targeted the Democratic plan for restricting spending on oxygen tank leases, removing a provision requiring proof of legal residence before children can receive SCHIP and slicing Medicare Advantage subsidies.

“None of those things I think are political winners,” Price said, calling the oxygen-tank provision “government-run health care at its worst.”

But Democrats, even conservatives, appeared to be falling largely in line.

Rep. John Barrow (Ga.), one of the most conservative Democrats, vowed to back the package on the floor, although he said he would prefer to close tax loopholes rather than raise the tobacco tax.

“I’m prepared to do what it takes to cover as many of the uninsured kids in my district and my state as we can,” Barrow said. “That’s what it’s all about.”

House Democrats also won votes of some of their conservatives when they cut the proposed tobacco tax in their bill from the 61 cents in the Senate package to 45 cents. That secured the vote of Rep. G.K. Butterfield (D-N.C.) and others.

“That’s why we did it,” House Majority Leader Steny Hoyer (D-Md.) said.

Meanwhile, there appear to be three factions on the issue within the 49-member Senate Republican Conference — complicating the leadership’s efforts to present a united front.

One Senate GOP leadership aide cautioned that Republicans could have “36 people holding tight” to sustain a veto. That’s two more than they need to prevent Democrats from reaching the 67-vote threshold needed to beat back President Bush’s veto pen.

But during this week’s Senate debate, Republican leaders — who oppose the bill — have to contend with a dozen or more GOP Senators who actually support the measure.

Plus, opponents of the bill are split into two camps — one that wants to use SCHIP to focus on the broader issue of reforming health care and one that wants to focus merely on what they see as the problems with expanding the existing program.

“Message-wise it’s tough,” acknowledged the Senate GOP leadership aide.

Among those who want a broad debate, Sen. Richard Burr (R-N.C.) said he wants to use the debate to “focus on fixing health care so that all of the Americans that are uninsured have an opportunity to be insured.”

Burr, along with GOP Sens. Bob Corker (Tenn.), Tom Coburn (Okla.) and Mel Martinez (Fla.), said he is likely to offer his bill to provide tax credits for buying health insurance as an amendment. Sen. Jim DeMint (R-S.C.) also supports the measure.

“We need to provide coverage for individuals that are uncovered, but the federal government is the most expensive way to accomplish that,” Burr said. “Understand, this is not an alternative to SCHIP. We’re all for SCHIP reauthorization. We’re just not for SCHIP expansion.”

Senate Republican leaders appear to be trying to pursue that nuanced message as well by cautioning that they actually do support SCHIP as it currently stands.

Senate Minority Leader Mitch McConnell (R-Ky.) is expected to offer the Republicans’ primary alternative as the party’s first amendment. The proposal would reauthorize SCHIP without expanding it to more children and includes provisions on small-business health plans and tax-free health savings accounts.

Like the Democratic measure, McConnell’s amendment also would force states to eliminate adults, who got coverage through Bush administration waivers, from the program. However, the Democratic version would require those adults to be phased in to Medicaid, the government-run health care program for the poor.

“We want the best possible health care for poor children, and right now the program is providing care for adults at the expense of those kids,” said Ryan Loskarn, spokesman for Senate Republican Conference Chairman Jon Kyl (Ariz.).

Given the Republicans’ apparent disarray, Senate Democrats said last week that they weren’t overly concerned about the GOP leadership’s efforts to dismantle the bill, considering Democrats are likely to have more than enough votes to block a filibuster.

“They don’t have an alternative,” Senate Finance Chairman Max Baucus (D-Mont.) said. “Theirs is ‘CLIP’: Children Lose Insurance Protection. … They’re clipping kids.”