Updated: 8:44 p.m.

With Democratic bickering threatening to imperil enactment of health care reform this year, President Barack Obama tried to stem the tide of intraparty unrest Wednesday by insisting that House and Senate leaders huddle at the White House until they had reached agreements on key issues.

Top party leaders and key committee chairmen emerged from a marathon negotiating session at the White House around 6:45 p.m. Wednesday night, but they planned to meet again Thursday without Senate Majority Leader Harry Reid (D-Nev.). Reid, who is expected to give a midday speech to the Geothermal Energy Association in New York City, has asked Senate Majority Whip Dick Durbin (D-Ill.) to stand in for him, sources said.

Obama, Reid and Speaker Nancy Pelosi (D-Calif.) issued a joint statement Wednesday evening, saying, “Today we made significant progress in bridging the remaining gaps between the two health insurance reform bills. We’re encouraged and energized, and we’re resolved to deliver reform legislation that provides more stability and security for those with insurance, extends coverage to those who don’t have coverage, and lowers costs for families, businesses, and governments.—

During the day Wednesday, Obama participated in much of the negotiating and “good progress— was made, one Democratic source said.

Obama’s stated goal to participants was that they come to a deal in principle on major sticking points in the health care overhaul, the source said.

“A lot of the heavy lifting is being done with the president in the room,— the source added.

Members and staff met for nearly eight hours Wednesday, with lawmakers and the president huddled in the Cabinet room and staff positioned next door in the Roosevelt Room. Everyone was asked to leave their cell phones and BlackBerrys at the door, the source said.

Administration participants included Vice President Joseph Biden and Health and Human Services Secretary Kathleen Sebelius as well as White House Chief of Staff Rahm Emanuel, Director of Legislative Affairs Phil Schiliro, and health care adviser Nancy-Ann DeParle.

Democratic aides said the primary sticking points going into the meeting were whether to tax high-cost, or “Cadillac,— insurance plans, how to deal with abortion language and whether to create a national, as opposed to state-based, insurance exchange.

House Majority Leader Steny Hoyer (D-Md.) spoke briefly to reporters Wednesday afternoon but refused to discuss details beyond noting that the whole health care package is being discussed — not just the House’s concern about the Senate’s proposed tax on the Cadillac health plans.

But opposition over that tax idea continued to bubble up among union leaders and a significant number of House Members, particularly lawmakers from high-cost areas whose districts would be disproportionately affected.

Union officials were at the White House in addition to House and Senate leaders, said Rep. Robert Andrews (D-N.J.), who was briefed on the meeting. Andrews said that affordability remains the top House demand, despite organized labor’s continued concerns about the Cadillac insurance tax.

Andrews quoted Ways and Means Chairman Charlie Rangel (D-N.Y.) as saying, “If they can’t buy it, I can’t sell it,— to sum up the problem of passing a health care bill with an insurance mandate if the plans are not affordable.

But Andrews praised Obama, saying the president had chosen the perfect time to get involved in the nitty-gritty of the bill. Democrats have been looking to get a bill to the president by February, but intraparty squabbling has reared its head in recent days, threatening to push that deadline off.

“He’s really got his sleeves rolled up,— Andrews said. “I think he’s picking the right moment to be engaged. … This will be a singular achievement for this president.—

Obama did appear to choose an opportune moment. House liberals have been publicly fretting about having to swallow the bulk of the Senate’s less ambitious health care bill, but Senate Democrats insist they have already squeezed as much compromise out of their moderates as possible and cannot move toward the more liberal House position on most issues.

“The House is upset with the perception that the Senate is getting its way,— said one senior Senate Democratic aide. “But no one can argue with the fact that the Senate bill cannot be changed much or otherwise we’re not going to get the votes.—

Like the House, the Senate passed its bill on a party-line vote, but Reid had to corral the votes of all 60 Members of the Democratic Conference in order to overcome a filibuster by the entire GOP caucus

House Democrats, however, were able to allow many of their Members to vote against the $1.2 trillion bill and still come out with a victory — and a single GOP vote. The House bill cleared in November, 220-215.

Indeed, Sen. Chris Dodd (D-Conn.) — a key health care negotiator who was at the White House on Wednesday — said on CNBC this week that the bill was “hanging by a thread— because one or two Senators could scuttle the bill. Dodd named moderate Sens. Ben Nelson (D-Neb.), Joe Lieberman (ID-Conn.) and Blanche Lincoln (D-Ark.) as Members who were particularly wedded to the Senate version as it currently stands.

Despite the House Members’ concerns, Senate aides have said the message House leaders have sent is that the Senate’s blueprint will be OK in the end — as long as there are some tweaks that will allow them to declare a modicum of victory.

“This is them starting a kabuki dance that will allow them to save face,— another senior Senate aide said of the noise on the House side.

Some Senate Democrats also warned House leaders may have to make even more concessions considering it is no longer a given that Massachusetts Attorney General Martha Coakley will be able to keep the late Sen. Edward Kennedy’s seat in Democratic hands. A potential upset by Republican Scott Brown in Tuesday’s special election would wipe out the Democrats’ current filibuster-proof supermajority in the Senate and steal a crucial vote away from the health care bill.

Though Democrats could try to delay seating a victorious Brown so that Kennedy’s temporary appointee, Sen. Paul Kirk (D), could provide the 60th vote for the bill, that scenario is fraught with political peril for both the White House and Democratic leaders, aides warned.

But Senate Democratic aides also said they could not yet envision a scenario where the House would simply pass the $871 billion Senate bill and send it to the president to become law.

The White House and Senate leaders have privately expressed a willingness to tinker with the Cadillac tax, even as they insist some taxes on high-cost plans will remain a part of the final package.

Rep. Joe Courtney (D-Conn.), who has led the fight against the tax, met with AFL-CIO President Richard Trumka on Wednesday morning, but said at that point there had been no concrete proposals made.

But Courtney said that one idea getting floated — a carve-out for union members — would not be enough on its own given the stark regional cost disparities between states and the fact that millions of middle-class families who do not belong to unions would still be affected.