“Three years ago, he was a strong proponent for universal health care, and I accused him of, after 20 years, dithering on that topic,” said Ned Lamont, the liberal Connecticut businessman who beat Lieberman in the 2006 Democratic primary but lost the general election. “As far as I can tell, a filibuster is one more dither, to quote the former vice president” (Dick Cheney).

Democratic insiders were less disappointed, saying Lieberman has been clear about his objections for weeks.

Reid “was not surprised by these comments,” said a Democratic leadership aide. “This has been [Lieberman’s] private view for months.”

Lieberman and Reid both acknowledged that he wasn’t the only Democrat with serious reservations about the public option, but the other members are fence sitters, not firm “no” votes like Lieberman. Sens. Ben Nelson of Nebraska and Evan Bayh of Indiana are among several Democrats who have left open the possibility of voting against Reid on procedural questions.

Reid, for his part, shrugged off Lieberman’s remarks, saying he had always factored in the senator’s concerns.

“I don’t have anyone that I have worked harder with, have more respect for in the Senate, than Joe Lieberman,” he said Tuesday afternoon. “As you know, he’s my friend. There are a lot of senators, Democrats and Republicans, who don’t like part of what’s in this bill that we sent over to [the Congressional Budget Office]. We’re going to see what the final product is. We’re not there yet. Sen. Lieberman will let us get on [to begin debating] the bill, and he’ll be involved in the amendment process.”

Senate Republicans — whose nearly unanimous opposition to all Democratic plans has put them on the sidelines — sought to portray procedural votes as up-or-down votes, invoking John Kerry’s much-ridiculed “flip-flop” on Iraq.

“I think it’s appropriate to make the point at the outset that a vote on cloture on the motion to proceed to this bill will be treated as a vote on the merits of the bill,” Minority Leader Mitch McConnell (R-Ky.) told reporters at the Capitol on Tuesday.

“We all recall Sen. Kerry’s strained way in the 2004 campaign of explaining why he voted for it before he voted against, and I think it is perfectly clear that most Americans will treat the vote to get on [with] the bill as a vote on the substance of the bill,” added McConnell.

Alexander Burns and Meredith Shiner contributed to this story.