Sen. Barbara Boxer (D-Calif.) said Monday she will not be intimidated by GOP boycott threats and vowed to begin marking up her climate change legislation Tuesday regardless of whether Republicans show up at the Environment and Public Works Committee session.

“The committee Republicans should rethink their approach. As long as they refuse to come to work, they are not participating in one of the most important issues facing our generation,— said Boxer, chairman of the EPW panel. She added, “If they do not, we will move forward in accordance with the rules of the Senate and of this committee.—

Republicans accused Boxer of attempting to steamroll her bill through the committee despite their requests for a complete new analysis of the legislation by the Environmental Protection Agency and warned that it could hurt the chances for an agreement in the future.

“I told her a long time ago that if we don’t get this analysis we weren’t going to be there for the markup,— ranking member James Inhofe (R-Okla.) said, adding that “this hurts their case. It’ll be much more difficult for them to come up with the votes. … It’s not smart.—

Inhofe has organized a boycott of the markup by all seven of the committee’s Republicans, a move that could force Boxer to break committee rules requiring two Republicans be present to hold a vote.

At the same time, six Republican ranking members of committees with jurisdiction over climate issues warned that could severely hurt the chances for an eventual bipartisan agreement.

“As the ranking members of the six committees that have jurisdiction over a great deal of the matters addressed by [Boxer’s bill], we felt it important to let you know that we are deeply troubled by the failure to accommodate a request … for a complete analysis of the bill’s projected impacts on the nation,— the six Republicans wrote in a letter to Boxer, adding that “as we are sure you will understand, from our viewpoint, such an approach would severely damage, rather than help, the chances of enacting changes to our nation’s climate and energy policies.—

In addition to Inhofe, signatories on the letter include Energy and Natural Resources ranking member Lisa Murkowski (Alaska), Agriculture, Nutrition and Forestry ranking member Saxby Chambliss (Ga.), Finance ranking member Chuck Grassley (Iowa), Foreign Relations ranking member Dick Lugar (Ind.) and Commerce, Science and Transportation ranking member Kay Bailey Hutchison (Texas).

But Democrats on the committee rejected Republicans’ complaints, noting that an analysis has already been performed on a companion bill in the House while defending their chairman against Republican attacks.

“Their behavior challenges everything we’re about here. … It’s almost like school children over there,— Sen. Frank Lautenberg (D-N.J.) said, quipping, “I’m not as gracious as Barbara Boxer is.—

Boxer said she has arranged for EPA officials to participate in Tuesday’s markup, and she would extend the deadline for GOP amendments until the end of Tuesday.

But she did not back down from her warning that the markup will proceed with or without Republicans, although she declined to discuss how she would work around the committee rules. “If we have to go that route, we’ll talk about how the committee would do that,— she said.

Despite the partisan theatrics, it remains unlikely that whatever Boxer’s committee passes will end up on the Senate floor until next year. Democratic aides have said part of the reason Boxer has pushed forward with a markup months before possible floor consideration is a result of leadership’s desire to have committee work on her version wrapped up while the nation’s attention is focused on health care reform.

As was the case of the health care bill — when the Health, Education, Labor and Pensions Committee moved an aggressively liberal version during last spring’s economic crisis — Democrats would like to move Boxer’s version now to allow other committees time to work on more moderate approaches, with an eye toward a final compromise being cobbled together by Majority Leader Harry Reid (D-Nev.) sometime next year.

Nevertheless, the dust-up on the EPW Committee clearly rattled lawmakers who are working on a number of other bipartisan climate bills, including Sen. John Kerry (D-Mass.), who is leading a bipartisan effort with Sen. Lindsey Graham (R-S.C.).

Indeed, Kerry sought to cool tensions on Monday afternoon, urging both sides to return to the table. “Over the years … we’ve made progress on climate change when we’ve been able to overcome partisan divisions,— Kerry said in a statement, adding, “I’d urge everyone to come back to the table, re-engage, and work together to move the process forward.—

“Nothing is falling apart. We’re proceeding ahead. … Sen. Graham and I feel confident in our ability to work with our colleagues,— Kerry said.

Kerry and Graham were scheduled to meet Wednesday with White House climate czar Carol Browner, Interior Secretary Ken Salazar and Energy Secretary Steven Chu to discuss the status of bipartisan talks and the possible outlines of a deal.

At the same time, President Barack Obama and his aides have been stepping up the public sales pitch and private lobbying to push climate change legislation out of committee and onto the Senate floor, even as the White House scrambles to craft a health care bill that can pass Congress.

“We sense there is some progress— on Capitol Hill, said one White House official in describing the administration’s growing effort. “Energy policy remains a high priority for the president,— the aide said.

Obama aides have insisted privately for weeks that they can push both health and energy this year, and that they do not see one effort detracting from the other. With Chief of Staff Rahm Emanuel absorbed in Afghan war deliberations and the health care reform lobbying campaign — which is still clearly Obama’s top priority — and top White House legislative aides also wrapped up in the health effort, other administration officials are taking the lead.

What Obama advisers refer to as the “Green Cabinet— has been helping lead the effort to find 60 votes in the Senate. The team includes Browner, Chu, EPA Administrator Lisa Jackson, Secretary of Agriculture Tom Vilsack and Salazar.

The group has met individually with more than half of the Senate, according to another White House official.

Obama himself has been talking at least as much about energy as he has about health care in recent days. For instance, at an Oct. 23 event in Boston, the president touted the various clean energy research projects being undertaken at the Massachusetts Institute of Technology.

Obama emphasized Republican participation in the process on Capitol Hill.

“We’re now seeing prominent Republicans like Sen. Lindsey Graham joining forces with longtime leaders John Kerry on this issue to swiftly pass a bill through the Senate,— he said.