Senior White House officials said Wednesday that they remain confident that House and Senate Republicans will remain unified behind President Bush’s opposition to setting a withdrawal date from Iraq and cast doubt on whether Democratic leaders ultimately could pass a supplemental spending package including one.

The comments come as House and Senate aides have begun preliminary talks on how to reconcile the two chambers’ differing versions of the supplemental. While the House version includes a hard deadline for withdrawal of troops from Iraq, the Senate version includes only a “goal” for a withdrawal by next March.

A senior Democratic aide in the Senate dismissed the chances that Congress will fail to pass a supplemental package including a timetable for withdrawal of some sort.

“I have no idea what they’re talking about, but if they think that, they’re sadly mistaken,” said Jim Manley, spokesman for Senate Majority Leader Harry Reid (D-Nev.). “The House and Senate share a common goal [of] trying to change course on Iraq. … We’ve barely begun having conversations about how to proceed.”

A top Bush aide noted that despite predictions of mass GOP defections over Iraq earlier this year, saying “We lost only four Republicans — two in the House and two in the Senate,” and said that Bush is confident Republican loyalty will hold during the upcoming vote on the supplemental spending conference report.

Although many on Capitol Hill have predicted the final conference report will mirror the Senate’s softer language on Iraq, this White House aide questioned that calculus.

Given the legislative gymnastics Speaker Nancy Pelosi (D-Calif.) performed to put together enough votes to pass the House version over the objections of Republicans and some liberals in her party, the aide argued it may be impossible for Pelosi to move substantially from her chamber’s version without putting her coalition in jeopardy.

Likewise, if Reid agrees to stiffer language, he could lose not only his two GOP backers — Sens. Chuck Hagel (Neb.) and Gordon Smith (Ore.) — but also moderate Democrats, notably Sen. Ben Nelson (Neb.).