Congressional liberals on Tuesday stressed their willingness to vote down a health care overhaul that lacks a robust government insurance plan, after White House Chief of Staff Rahm Emanuel suggested such a plan could be delayed.

Rep. Raúl Grijalva (D-Ariz.), co-chairman of the Congressional Progressive Caucus, wrote a letter to President Barack Obama saying he read “with alarm and dismay— Emanuel’s comments in Tuesday’s Wall Street Journal that a trigger could be included in the health care overhaul that would result in a government-run plan down the road, but only if sufficient competition does not develop in the private market.

“I want to be clear that any such trigger for a strong public plan option is a non-starter with a majority of Members of the Congressional Progressive Caucus,— Grijalva said. “As the CPC has repeatedly stated, its Members cannot support final passage of any health care reform bill that does not include a robust public plan option, akin to Medicare, operating alongside private plans.—

Grijalva added that it was “unacceptable— for any negotiated cost savings with hospitals and other providers to be contingent on ditching the public plan.

But conservative Democrats cheered the opening provided by Emanuel.

Rep. Mike Ross (D-Ark.), chairman of the Blue Dog Health Care Task Force, issued a statement backing the trigger idea discussed by Emanuel.

“A proven effective method of increasing competition and choice in the marketplace is to require that private industry adopt reforms in order to meet specific availability and cost targets,— Ross said. “Failure to meet these goals would then trigger a public option that would compete on a level playing field.—

Emanuel’s comments effectively poked a sharp stick into the thorniest philosophical divide among Democrats. House liberals have repeatedly threatened to vote down any bill that includes a trigger, while Blue Dog Democrats strongly support a trigger and may not support a bill without one.

The issue also is a bright line between Senate Democrats and Republicans, who oppose a public plan en masse.

Obama early Tuesday sent out an unusual statement reaffirming his support for a public plan — although without directly refuting Emanuel’s comments.

“I am pleased by the progress we’re making on health care reform and still believe, as I’ve said before, that one of the best ways to bring down costs, provide more choices, and assure quality is a public option that will force the insurance companies to compete and keep them honest,— Obama said in a statement.

House Republicans seized on Emanuel’s comments to try to undercut support for the House Democratic bill, which includes a robust public health plan based on Medicare.

“How will Mr. Emanuel — who suggested to the Wall Street Journal that a massive, government-run option will be dropped from the final bill — look any Member in the eye and ask them to take that politically tough, and utterly pointless, vote?— asked Michael Steel, spokesman for House Minority Leader John Boehner (R-Ohio).

Emanuel was set to meet with House Democrats after press time Tuesday night.

Emanuel’s remarks also caused an uproar among some of the president’s strongest supporters, including MoveOn, which blasted Emanuel’s comments and urged its members to call the White House and complain.

“Right now, when key committees are finalizing health care legislation, Emanuel’s remarks will only embolden conservative opponents of reform,— MoveOn told its members. “He should be standing with the majority of Americans for a strong public health insurance option — not disastrous half-measures like the trigger.’—

Other grass-roots supporters of Obama’s health care initiative had a more muted reaction after the White House quickly churned out Obama’s statement. The statement came out a little after 10 a.m., just a few hours after Emanuel’s comments began filtering through Democratic circles.

Officials with Health Care for America Now — a broad alliance that includes the leading unions, activists groups like the Campaign for America’s Future, the National Council of La Raza and MoveOn, and the Democratic think tank Center for American Progress — said they are taking Obama at his word that he strongly backs a public insurance option.

“President Obama has been very consistent about his support for a public insurance option,— alliance spokeswoman Jacki Schechner said. But she said her group is firmly opposed to the idea mentioned by Emanuel of a “trigger— that would bring a government option into play when competition between private plans is insufficient.

“It has to be national and [in effect] on Day One,— Schechner said of the public option.

The White House did not respond to requests for comment by press time.