The White House's signal that it's willing to back off support for a public health insurance option has sent congressional liberals into full revolt, bluntly warning the administration that no legislation will pass without a government-run plan.

(L-R) Reps. Raul Grijalva, Anthony Weiner, Barbara Lee and Anna Eshoo want a public health option. (Photo: AP photo composite by POLITICO) A group of left-leaning House Democrats tells POLITICO that a bill without a public option simply won't win enough votes in their caucus - a sentiment that raises fresh questions about the prospects to enact sweeping health care reform this year.

"A bill without a public option won't pass the House," said Rep. Anthony Weiner (D-N.Y.), a member of Energy & Commerce Health subcommittee. "Not only are they weakening their proposal, but they are also weakening their hand. This is legislative subtraction by subtraction."

Privately, the leaders of the Congressional Progressive Caucus and Congressional Black Caucus sent the same message to Health and Human Services Secretary Kathleen Sebelius, who said Sunday that a public plan is "not the essential element" of comprehensive reform.

"To take the public option off the table would be a grave error; passage in the House of Representatives depends upon inclusion of it," wrote Reps. Raul Grijalva (D-Ariz.), Lynn Woolsey (D-Calif.) and Barbara Lee (D-Calif.) in a letter to Sebelius Monday.

Along with their sharply worded letter, the three House members sent an attachment listing the "60 Members of Congress who are firm in their position that any legislation that moves forward through both chambers, and into a final proposal for the president's signature, MUST contain a public option."

Even if top aides didn't intend to do it, the White House got a glimpse of what may well happen - a Democratic civil war - if President Barack Obama does indeed give up on the public option.

The liberal uprising comes after weeks in which Democratic congressional leaders have focused their energy on winning over moderates - with House leaders trying to woo Blue Dog fiscally conservative Democrats, and Senate negotiators concentrating on a handful of Republicans.

Obama also has been put on the defensive by conservatives who have dominated congressional town halls, saying Obama's government-run insurance goes too far.

But the weekend's events show that one of Obama's biggest problems - and ultimately a critical test of whether he can get a bill at all - revolves around convincing liberals he's going far enough.

Rep. Anna Eshoo (D-Calif.), a member of the Health subcommittee and a close friend of House Speaker Nancy Pelosi, said a healthcare bill without a government-run insurance plan would be difficult to move out of the House in part because liberals are right now accepting less than what they want.

"I think it would be very tough," said Eshoo. "There are those who view themselves as having already compromised on single-payer."

Of the message from the White House over the weekend, Eshoo said, "My sense is that there's a deep disappointment on that, the softening position on that."

Added Rep. Eliot Engel (D-N.Y.), another member of the Health panel: "Without that [public] option there will not be enough votes in the House to pass that bill."

The White House continued to insist Monday that the widely reported shift away from the public option was no shift at all - that Obama still believes it is the best way to provide needed competition with private insurance companies. Yet Obama himself on Saturday called the public plan just a "sliver" of the overall package, followed by Sebelius' comments that it wasn't essential.

Liberal advocacy groups took the rhetorical shift -- deliberate or not -- as a warning shot.

Democracy for America honed in on the 60 House members who have pledged not to vote for a bill without the public option, and asked supporters to remind them to hold firm. Health Care for America Now urged its network to contact senators. And the Progressive Change Campaign Committee promised a new round of TV ads targeting undecided senators and highlighting their contributions from health and insurance interests.

"There is zero retreat on the grassroots level for the public option. We are all in, and we're staying all in, because the public option is the compromise," said Adam Green, co-founder of the Progressive Change committee, one of the most aggressive defenders of the public option.

"If Kathleen Sebelius, Rahm Emanuel, or anyone else thinks the grassroots will rally behind anything short of a strong public option, that would be a serious miscalculation," Green said.

The White House is clearly betting that liberals simply won't walk away from a health-reform bill that achieves most of what Democrats want, such as expanded coverage, affordability and limits on some insurance company practices, including dropping people when they get sick. But former Democratic national chairman Howard Dean is urging Democrats to do just that - to put off health reform this year if they can't get the public option.

The damage to Obama from such a move would be significant, a sign that he didn't have the political capital to push his top legislative priority through a Democratic Congress. For the party, it could send a signal to voters that Democrats are too fractious to govern effectively ahead of the 2010 midterms.

To liberals, however, the bigger question is the reverse: why should the party retreat from a government-run insurance option simply because Democratic moderates -- or worse, Republicans -- don't like it? They suggest Obama, long a darling of the Democratic left, would suffer the consequences.

"It would likely result in a plummeting of this administration's popularity among their base, depressed turnout in 2010 except in Democratic primaries, and a well-deserved loss by any Democrat in Congress who puts insurance companies ahead of the overwhelming majority of Americans who want the choice of a public option," Green said.

Rep. Jan Schakowsky (D-Ill.), another member of the Health subcommittee, said she was reassured by the White House message to allies that "nothing had changed," but added: "I think it important that the president make clear his support for the public option."

Recognizing the concern in her caucus, Pelosi issued a statement Monday afternoon that noted: "There is strong support in the House for a public option."

House Democrats also are growing increasingly agitated at what they see as the Senate's outsized role in the healthcare debate. Liberals are especially wary of the Finance Committee, the only congressional panel that has yet to pass health care legislation and where support for a public plan is weakest.

"The Senate needs to understand that they are one-half of the process, not the entire process," said Engel. "This is not a matter of [Senate Finance Committee Chairman Max] Baucus or anybody else negotiating a bill, than coming to the House and saying, ‘take it or leave it.' That's not how it works."

Rep. Frank Pallone, chairman of the Energy & Commerce Committee's Health Subcommittee, said the House wouldn't just roll over to whatever compromise the Senate comes up with.

"As far as we're concerned, we're going to pass as strong a House bill as possible," Pallone said. "I don't buy into this option that we're just going to buy into the Senate bill. We're going have to have a true conference committee."

The message from these House Democrats puts them at odds with some of their Senate counterparts, such as Sen. Kent Conrad (D-N.D.), who are saying just the opposite about the political calculus in their chamber - that a plan that does include a public option won't pass the Senate.

The reaction in the Senate was far more muted Monday, with only a handful of public statements. Sen. Russ Feingold (D-Wisc.) suggested he could withhold support, saying he is "not interested in passing health care reform in name only."

Beyond Congress, the comments from the administration and senators like Conrad have roused some liberals who have been splitting their time between counter-punching conservative opponents of the bill and taking on recalcitrant Democrats.

"It's a reminder to all of us that we have to stick with this and approach it like a campaign," said Jim Dean, head of Democracy for America and Howard Dean's brother. "I wasn't necessarily unhappy with the statements. It just told me we've got to get to work."

Doing just that, Jim Dean sent an email to Democracy for America's email list Monday that stated in bold: "A Healthcare bill without a public option is D.O.A. in the House. Period."

According to a whip count by Open Left, a liberal blog, 43 senators support the public option. "So the question is, how do you build a majority on the public option?" said HCAN's Richard Kirsch said. "You can't have a situation where a minority of folks are dictating the whole package."

For all their concern about the weekend's events, House Democrats made clear that the battle was only beginning.

"Keep in mind that we have a long, winding road before anything solidifies," Eshoo said.