Senate Democrats are looking to build firewalls between their legislation reauthorizing transportation programs and the Keystone XL pipeline, which House Republicans will push hard for in the upcoming conference committee. And Republicans will likely have an ally on Keystone in a Democratic conferee, Senate Finance Chairman Max Baucus (Mont.).

Senate Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) appointed conferees Tuesday, and their House counterparts are expected to do the same today. But the path to approving a final bill is unclear and rocky. The Senate passed its two-year legislation on a 74-22 bipartisan vote. The House struggled for months to arrive on a legislative vehicle, finally approving a short-term extension last week just to get to conference.

“Our bill is so good, it’s just astounding. It’s got so much safety stuff in it. It’s got money in it,” said Senate Commerce Chairman Jay Rockefeller (D-W.Va.), a conferee. “Theirs … has no money. It’s not comparable.”

The House included in its measure language fast-tracking the pipeline. President Barack Obama has already threatened to veto any transportation legislation that includes such language. The pipeline has Democratic support in both chambers, but none as powerful as Baucus’.

In a payroll conference committee earlier this year, Baucus worked counter to leadership and the administration, negotiating ways to approve the pipeline and engaging in talks with Sen. John Hoeven (R-N.D.), who was named to the conference committee by McConnell on Tuesday.

Senate Democrats might have some cushion among their ranks, however. Leaders agreed to a larger conference, and Senate Democrats on the committee outnumber Republicans, 8-6, leaving room for Baucus to defect over the pipeline and to not jeopardize Democratic approval.

Fighting over Keystone has become part of the game during the past few months. Republicans have brought construction of the pipeline into several legislative fights. They have used it to criticize the administration, which has an expedited request to consider the pipeline once this year, by linking it to job creation.

Reid said he, like the president, is unmoved by Republican arguments on the issue.

“Have we had a provision come up here in the past six months where it hasn’t been put in? Keystone’s virtually been put in everything. I’m not going to be negotiating what’s going to be in this bill today,” Reid said after his Conference’s weekly lunch. “I have eight great Senators who are going to be working on a final package. Personally, I’m not one of the conferees, but personally, I think Keystone is a program that I’m not going to help in any way I can, and the president feels that way, too.”

Rockefeller also added he would not support the Keystone language. “There probably would be a few,” the West Virginia Democrat said of colleagues who might support the project. “I will not be one of them.”

Of the 11 Senate Democrats who have voted in favor of the pipeline, only Baucus is on the conference committee.

As for the overall negotiations, sources were not clear on how long the process might take and were reluctant to handicap the chances for success without knowing whom House leaders were planning to appoint.

Congress is slated to be in recess next week, so talks on the Member level likely will not begin in earnest until they return, though staff-level negotiations probably will commence earlier.

The most significant question facing the panel, regardless of which Republicans Speaker John Boehner (Ohio) appoints, will be how to construct a package that can pass a House shaped by conservative Republicans eager to cut government spending.

Just because Senate Republicans largely supported the bill that cleared their chamber does not mean their House counterparts will be satisfied with a conference report that resembles it at the end of talks.

The Senate bill, championed by Environment and Public Works Chairman Barbara Boxer (D-Calif.) and ranking member James Inhofe (R-Okla.), consolidated almost 200 federal transportation programs into about a dozen and maintained the current scope of transportation and infrastructure projects. Boxer and Inhofe are both conferees.

Aides from both parties suggested McConnell also would like to see a successful conference report. Senate Republicans were burned by their House counterparts at the end of 2011 when the House GOP backed off a two-month payroll tax cut agreement McConnell struck with Reid. Republicans were largely viewed as the losers after the intraparty snafu, and some suggested Senate Republicans especially would like to avoid a repeat occurrence.

Moreover, aides indicated that even if the GOP were to lose out on the addition of Keystone language in this round, it would not come out as a net loss for the party. Republicans could continue to use the Keystone project as a weapon against Democrats as the general election continues to heat up and the GOP tries to win back both the Senate and the White House.