House Democratic leaders released a sweeping health care overhaul Tuesday with a strong endorsement from President Barack Obama, but they acknowledged they still have much work to do to bridge intraparty differences and get a bill passed by August.

“This legislation is landmark legislation, and this is a defining moment for our country,— House Energy and Commerce Chairman Henry Waxman (D-Calif.) proclaimed.

Waxman said Democratic leaders are trying to find common ground. “We all have to come together, compromise and work out our differences,— he said, warning that he’s prepared to stick around for the upcoming recess to get the bill finished.

“We quite frankly cannot go home for a recess unless the House and the Senate pass bills,— Waxman said.

The House Democratic bill was unveiled as that pressure rose to pass separate bills out of the House and Senate before Members leave town for August. Senate Finance Committee Democrats are working furiously to unveil a bill by Thursday to get on track with the House’s more expedited schedule.

But both chambers face an uphill climb quelling intraparty concerns over the shape of the bill and how to pay for an overhaul. Last week, Speaker Nancy Pelosi (D-Calif.) and House Majority Leader Steny Hoyer (D-Md.) huddled for two hours behind closed doors with conservative Blue Dog Democrats worried that a massive health package would cost too much and create a new government-run insurance plan. Pelosi met with them again late Tuesday to try to mollify their concerns.

Obama, who some had accused of staying on the sidelines in the debate, provided much-needed cover for House Democrats, offering a strongly worded statement of support for the bill Tuesday.

“The House proposal will begin the process of fixing what’s broken about our health care system, reducing costs for all, building on what works, and covering an estimated 97 percent of all Americans,— Obama said. “And by emphasizing prevention and wellness, it will also help improve the quality of health care for every American.—

But Obama didn’t mention the numerous tax increases added to pay for the House Democrats’ bill, including one on families making more than $350,000 a year, a “pay or play— tax on businesses that don’t provide health insurance and a tax increase on families that do not buy health insurance — a mandate Obama opposed during the presidential campaign.

Democrats have been urging Obama to specifically embrace the tax plans to aid Members in conservative districts. There also is significant trepidation on the part of vulnerable Democrats that they will be asked to back a series of tax increases that will be rejected by the Senate. The Senate Finance Committee has yet to agree on how it plans to pay for its bill.

The three House Democratic chairmen who wrote the legislation will also face significant attempts to change the bill in committee markups that begin Thursday.

Rep. Mike Ross (D-Ark.), leader of the Blue Dog health care task force, said his group would continue to push for cutting costs.

“Reform that does not meet the President’s goal of substantially bringing down costs is not an option,— Ross said in a statement.

Pelosi backed the effort to find more cuts.

“We want to squeeze every dollar we can out of the system,— she said.

Blue Dogs also are demanding additional aid to rural areas. And the government-run insurance option, which would be available as part of a national health insurance exchange, still faces concerns across the Caucus, but particularly from Blue Dogs and moderate New Democrats because its rates are tied to Medicare, which they argue pays too little in many regions of the country.

The Democrats’ legislation, meanwhile, came under withering criticism from business groups including the National Federation of Independent Businesses and the U.S. Chamber of Commerce.

Not surprisingly, House Republicans jumped on the plan — even sending out missives during the Tuesday afternoon Democratic press conference. They blasted it as a job-killer and said it amounts to a government takeover of health care.

“During a deep economic recession, it is criminal malpractice for Democrats to push a government takeover of health care and a new small business tax that will destroy more American jobs,— House Minority Leader John Boehner (R-Ohio) charged.

Rep. Roy Blunt (Mo.), who chairs the GOP Conference’s health care task force, said he would offer an amendment in committee that would require all federal elected officials to enroll in the new government-run plan.

“If they think a tax-raising, job-killing, access-limiting plan is good enough for the people they represent, then it ought to be good enough for them too,— Blunt said.

However, much of the bill’s impact would not happen for several years, according to the Congressional Budget Office. The income tax increase on the wealthy — which ranges from 1 percent for those with incomes of more than $350,000 to a 5.4 percent tax for those earning more than $1 million, would not take effect until 2011. And new tax credits and the national health exchange would also take years to implement.

The tax increase on the wealthy would raise more than $544 billion, and savings in Medicare are expected to top $500 billion, with insurance companies, hospitals, drug companies and other providers being asked to help pay for health care for the uninsured and to close the “doughnut hole— for seniors.