by Greg Sargent (The Plum Line)

In a letter delivered to the White House moments ago, the two leaders of the bloc of House progressives bluntly told President Obama that they will not support any health care plan without a public option in it — and demanded a meeting to inform him face to face.

The not-yet-released letter — the first joint statement from progressives since news emerged that Obama might not address the public option in next week’s speech — is their sharpest challenge yet to the president, given the extraordinary sensitivity of this political moment. The letter urges him to mention the public option in his speech.

“Any bill that does not provide, at a minimum, a public option built on the Medicare provider system and with reimbursement based on Mediare rates — not negotiated rates — is unacceptable,” reads the letter, which was sent over by a source. It was signed by Reps. Lynn Woolsey and Raul Grijalva, the two leaders of the Congressional Progressive Caucus.

“A health reform bill without a robust public option will not achieve the health reform this country so desperately needs,” the letter continues. “We cannot vote for anything less.”

“We look forward to meeting with you regarding a robust public option in any final health reform bill and request that that meeting take place as soon as possible,” the letter says.

Last month, five dozen House liberals wrote a letter to Nancy Pelosi ruling out support for any bill without the public option. While today’s letter doesn’t bear all those signatures, it signals that House progressive leaders intend to try to maintain a united, potentially confrontational front even as the president prepares to make his case in a major, make-or-break address to Congress.

Should Obama jettison the public option, progressives will come under tremendous pressure to back the plan anyway. White House advisers will likely insist that liberals mustn’t deny the president a historic victory and enable a defeat that could cripple the first African-American presidency.