Though negotiations on a second version of the supplemental Iraq War spending bill likely won’t begin in earnest until later today, Democrats and Republicans on both sides of the Capitol began staking out their starting positions as they race against the clock to send President Bush a bill by Memorial Day.

Senate Majority Leader Harry Reid (D-Nev.) struck a defiant tone at a press conference Wednesday, even as he pledged to work in “good faith” with Republicans on Capitol Hill and at the White House.

“Democrats are not — I repeat, not — going to allow a blank check to the president. That’s not going to happen,” Reid said. He continued, “I think the president has learned enough from the debate that’s taken place in the last week here in Congress and with the American people that he shouldn’t try to push us in that regard.”

Democrats were unsuccessful in their first attempt to set limits on the president’s management of the war. Bush vetoed the original supplemental war spending bill setting a timeline for withdrawal from Iraq.

Still, Reid said he hopes to resume talks with White House Chief of Staff Josh Bolten and Senate Minority Leader Mitch McConnell (R-Ky.) today, shortly after the Senate passes a “placeholder” bill that does not fund the troops but will allow the Senate to request a conference with the House on the war spending bill. (The House bill would fund the war until July, when Congress would have to vote again to release the remaining funding for this fiscal year.)

Reid said he was looking forward to including Speaker Nancy Pelosi (D-Calif.) in the talks over how to establish benchmarks for the Iraqi government and what consequences, if any, there should be for the Iraqis’ failure to meet them.

“I have my best fighter now — I have Pelosi — that’ll back me up, and that’s going to be a great comfort to me because all my negotiations at this point have been with Bolten and McConnell alone,” he said.

For their part, House Democrats have acknowledged the need to compromise, despite having to deal with a strong liberal element in their Caucus that wants the United States to withdraw from Iraq and is reluctant to vote for anything that continues to fund the war. But rather than having that fight again on the supplemental, Democratic leaders in the House are eyeing the fiscal 2008 Defense spending bill as their next opportunity to try to force the president’s hand.

Meanwhile, Senate Republicans signaled that their starting position for negotiations would be Sen. John Warner’s (R-Va.) proposal that garnered 52 votes on Wednesday, including the support of eight largely centrist Democrats. The majority of Democrats, and three Republicans, voted against the proposal, with Democrats saying it did not go far enough in forcing the president to change his strategy for the war.

The Warner proposal would allow the president to withhold reconstruction funds if Iraqis did not meet certain benchmarks that would help them address the sectarian rift in the country and their ability to take over military and security duties.

Calling Warner’s amendment “a responsible middle ground,” McConnell said the proposal “could well be a part of a final conclusion on the supplemental appropriation[s]” bill.

Democrats viewed that vote differently, saying GOP support for Warner’s amendment showed that “many Republicans are getting nervous about supporting this president blindly,” according to Senate Majority Whip Dick Durbin (D-Ill.).

But Reid made clear that the Warner language was “pretty weak” in his estimation, and Senate Democratic Caucus Vice Chairman Charles Schumer (N.Y.) said Warner’s proposal was “not good enough. … We have to have a resolution that has teeth in it.”

No one disagreed, however, on the need to finish up negotiations by the end of next week — a prospect that most agreed was feasible, but potentially fraught with partisan mistrust.

“On the conservative side, many are very leery of things being worked out in conference,” said one Senate GOP aide, “because Reid and Pelosi control what happens and you’re left with an up-or-down [vote] on a final product.”

Senate Democratic and Republican leaders were more optimistic.

“It won’t be easy to get an agreement in conference that the president can sign,” said Senate Minority Whip Trent Lott (R-Miss.). “But I believe our leaders are committed to that, and they’re making progress.”

Steven T. Dennis contributed to this report.