Senators emerged from a bipartisan meeting at the White House with President Barack Obama on Tuesday with mixed messages about how to advance climate change legislation.

Sens. Joe Lieberman (ID-Conn.) and John Kerry (D-Mass.) told reporters that Obama made a “very passionate” argument in favor of a carbon tax and described a “breakthrough” when a number of Republicans indicated they would be open to a pared-back version of cap-and-trade energy legislation.

“Some of our colleagues who up until this time have been at least publicly reluctant about … putting a price on carbon pollution said they would be willing to discuss limited forms of doing that in this bill,” Lieberman said. “Sen. Kerry and I want to begin to take advantage of this by sitting and talking with those colleagues across party lines as quickly as we can.”

Kerry and Lieberman are co-sponsoring of a comprehensive climate change measure that is currently idling in the Senate.

Lieberman said he is “not naive about the difficulty in an election year” of trying to advance sweeping energy legislation, but said he left the meeting feeling “optimistic and encouraged … that we can make something very good happen.”

Kerry said Democrats will be trying to nail down a bipartisan proposal “over the course of the next weeks,” although he dodged questions about a timeline for passing a bill.

“All of us have to compromise. We believe we have compromised significantly, but we’re prepared to compromise further,” Kerry said. “We are prepared to scale back the reach of our legislation in order to try to find that place of compromise.”

But Republican Sens. Lamar Alexander (Tenn.) and Lisa Murkowski (Alaska) told reporters that they drew a line in the sand in terms of supporting any energy bill with cap-and-trade provisions.

“As long as we take a national energy tax off the table, there’s no reason we can’t have clean energy legislation,” said Alexander, chairman of the GOP Conference.

“Americans are focused on jobs,” said Murkowski, the Conference vice chairwoman. “That is the reason that a cap-and-trade proposal, a national energy tax, will not sell in this country at this time.”

At least one Republican in the meeting, Sen. Judd Gregg (N.H.), suggested that his party may be willing to compromise, however.

There was “more common ground than disagreement” in the meeting, he said. “There is the opportunity to do an energy bill here.”