A public break with the White House’s war strategy by one of the Senate’s most respected Republican foreign policy voices signaled potentially far-reaching new troubles ahead for President Bush.

Richard G. Lugar of Indiana, the ranking Republican on the Senate Foreign Relations Committee, took to the Senate floor Monday evening to deliver a grim assessment of Bush’s Iraq policy and to call for an immediate drawdown of U.S. forces there. He said Bush’s deployment of additional U.S. troops to Iraq was unlikely to produce positive results by September, when a report by Gen. David H. Petraeus, the top commander in Iraq, is due.

Until now, Lugar, like many other Republicans, had been privately skeptical of Bush’s stewardship of the war but publicly urged that the president be given time for his strategy to work. With his speech, however, he gave voice to the growing doubts among Republicans.

Indeed, George V. Voinovich, R-Ohio, also a member of the Foreign Relations panel, sent a letter to Bush on Tuesday echoing Lugar’s calls for a reduction of U.S. forces in Iraq and renewed diplomatic efforts to stabilize the Middle East.

“We must begin the process now,” Voinovich said in a strategy paper that accompanied his letter to Bush.

John W. Warner, R-Va., the former chairman of the Senate Armed Services Committee, who warned last October that the war in Iraq was “drifting sideways,” said he expected Lugar’s speech to add steam to the vigorous Iraq debate during consideration of the fiscal 2008 defense authorization bill (S 567, HR 1585), something expected to take place after the July Fourth recess.

The debate is expected to coincide with the July 15 release of an interim report on the Iraq War.

Warner has said he is considering an amendment that would rewrite the 2002 authorization for the war. As long ago as last August, Warner said the resolution (PL 107-243) had been overtaken by events in Iraq.

“I hail what he did,” Warner said of Lugar’s speech. “It shows the strength that each of us individually must bring to this debate.”

Warner, who commands enormous respect as an expert on military affairs, said he agreed with Lugar that the September reporting date is too long to wait to revise U.S. war policy and that Lugar’s speech captured the sentiments of many other lawmakers.

“He’s drawing on many of the principles that many senators have expressed,” Warner said.

Some political analysts said they were more surprised by Lugar’s refusal to speak up earlier against Bush’s handling of the war than by the June 25 speech. They said he had ample opportunity during hearings he held on the issue during the last Congress, but his GOP loyalties apparently held him back.

Andy Fisher, a spokesman for Lugar, said the speech did not mean that the senator would switch his vote on supporting the war or embrace Democratic measures setting a deadline for U.S. troop withdrawal.

“Lugar feels that moving the president and Congress constructively in a bipartisan way is still possible in the plan he outlined,” Fisher said.

White House spokesman Tony Snow praised Lugar as a “serious guy,” but rejected his advice, appealing to lawmakers to give Bush’s strategy more time to succeed.

“Dick Lugar is giving what he thinks is his best advice, and we certainly appreciate it and take it seriously, but we also believe that it is very important to go ahead and let the surge, No. 1, finish getting put in place, and second, let’s see what results it produces,” Snow said.

Democrats, who have lacked the votes in the Senate to pass legislation that would constrain Bush on Iraq, applauded Lugar’s remarks.

“Some floor speeches go unnoticed, but Sen. Lugar’s is not one of them,” Majority Leader Harry Reid, D-Nev., said in a floor speech Tuesday. “When we finally end this war and the history books are written, I believe Sen. Lugar’s words yesterday could be remembered as a turning point. But that will depend on whether more Republicans take the courageous first step that Sen. Lugar took last night.”

A day after Lugar’s speech, however, its impact on conservative Republicans was unclear. Jeff Sessions, R-Ala., acknowledged that there was growing sentiment in the Senate that the U.S. presence in Iraq needed review and that troop levels should be reduced “as soon as it is realistic to do so.”

But Sessions said that moment had not yet arrived and that he still wanted to give Bush’s “surge” strategy a chance to work. “It hasn’t failed yet,” he said.

At least one GOP moderate also played down the significance of Lugar’s speech. “I think he’s talking about planning,” said Norm Coleman, R-Minn., a member of the Foreign Relations Committee. “There’s not a lot new in that.”

Political analysts said such remarks reflect the view among some Republicans that Lugar is too moderate to lead opinion on the war within their caucus.

“I don’t think he’s the one who would presage the collapse of Republican support for the war,” said Thomas E. Mann, a government scholar at the Brookings Institution.

But other experts said Lugar’s speech carried major political significance.

“We are at the cusp of a trend, in which Republicans are looking at the situation in Iraq and not seeing any real reason to believe the surge is succeeding, especially when it comes to bringing about political reconciliation,” said Bruce Riedel, a former Middle East expert at the CIA and National Security Council.

On Tuesday, Lugar said it was important to begin the revision of U.S. war policy now, before the political climate heats up heading into the 2008 elections and bipartisan agreement becomes impossible.

“The purpose of giving this speech now is that we are in a quiet period, when we are not forced into extreme debates, and there can be consensus building,” he said.

Lugar said he did not blindside Bush with his speech, noting that he had told the president his views privately in January. He said he would meet with administration officials later this week to push for a policy shift, but did not plan any specific legislation to advance his views.

Sen. Evan Bayh, D-Ind., said Lugar’s speech was not driven by pressure from their constituents, but rather by a thoughtful evaluation of the situation and the nation’s broader national security interests.

As chairman of the Foreign Relations Committee in the 109th Congress, Lugar held more than 30 oversight hearings that probed U.S. efforts there. He publicly supported Bush’s refusal to set a timetable for a U.S. troop withdrawal, while quietly expressing growing skepticism over the president’s war strategy.

Patrick Yoest and Tim Starks contributed to this story.