Iowa Sen. Tom Harkin, the Democrat who chairs one of the Senate committees tasked with developing health care legislation, promised Friday that a health care bill will be on President Obama's desk before Christmas and will include a so-called "public option."

"I believe we are in an irrevocable position," Harkin said on a conference call organized by the health care reform group Families USA. "The momentum is there. We will not get stopped by the obstructionists. We will have the votes."

Harkin became chairman of the Health, Education, Labor and Pensions Committee after the former chairman, the late Ted Kennedy, passed away in September. His committee has already passed a more liberal version of the health care bill that includes a public option — legislation that will have to be merged with the bill that passed the Senate Finance Committee earlier this week before the Senate can vote on final legislation. Democrats need sixty votes to end debate before a vote can held.

Pointing to a Thursday meeting of Senate Democrats in which most members of the caucus expressed support for a government-run insurance plan, Harkin said only five members of his party are holding up progress toward a such a plan.

"Should the five come on board with the vast majority?" Harkin asked. "I think the answer is clear."

But Harkin also said he was open to legislation that includes health care co-ops, as long as they are offered as a choice alongside a public option.

The Iowa Democrat estimated the final health care bill should cost $900 bill over 10 years and will mandate that all Americans purchase some kind of health insurance.