Senate leaders began substantive negotiations today with White House chief of staff Joshua B. Bolten in hopes of completing a stalled war spending bill before the Memorial Day recess in three weeks.

After striking a combative posture for several weeks, Senate Democrats sounded a note of compromise as the discussions got under way, and even though they said a timetable for withdrawal of troops is “not off the table,” they admit that benchmarks and potential presidential waivers for a timetable are more likely to appear in the new spending bill.

Senate Majority Leader Harry Reid, D-Nev., and Minority Leader Mitch McConnell, R-Ky., met with Bolten for 45 minutes, and Reid described the session as “constructive” although he offered no specifics about the meeting.

Later, Bolten and Budget Director Rob Portman conferred with House Minority Leader John A. Boehner and Jerry Lewis, ranking Republican on the Appropriations Committee.

From there, the White House negotiators went to the basement of the Capitol for a private meeting with Lewis, R-Calif., and Appropriations Chairman David R. Obey. “We just talked for a while. Nothing was decided,” Obey, D-Wis., said afterward.

The challenge for Democrats — now that they have failed to override President Bush’s veto of a $124 billion spending bill (HR 1591 — H Rept 110-107) with a withdrawal timeline — is to craft benchmarks for the Iraqi government that are enforceable yet do not force a withdrawal.