GOP leaders in the House and Senate and the Bush Administration have been unable to come to terms on a funding level for the bill, which pays for all federal highway construction.
The White House has insisted on a bill no larger than $275 billion, but both the House-approved version ($284 billion) and Senate bill ($318 billion) are remarkably higher, promoting a veto threat.
A meeting between House and Senate GOP leaders and White House Chief of Staff Andy Card on the issue Tuesday failed to produce a compromise.
Senate Environment and Public Works Chairman James Inhofe has indicated that Republicans as well as Democrats would be included in the conference, potentially allying fears among some Senate Democrats that they would be excluded from the negotiations.
Senate Democrats have so far blocked efforts to move to conference with the bill, citing their being shut out of compromise talks by GOP leaders in the past.
The White House is also expected to participate in the discussions.