That Bush needs some kind of political boost is unarguable after nine months of almost unremitting bad news, starting with the mishandling of Hurricane Katrina and continuing through the wrangling over immigration policy.

“Our first reaction ought to be that it's nice to see monsters eliminated,” said Thomas Mann, a veteran political analyst at the Brookings Institution. “But I do expect to see a little boost for the president because of this. It changes the story line, which is nice for him.”

Bush's subdued reaction in announcing al-Zarqawi's death was widely noted.

Lee M. Miringoff, director of the Marist Institute for Public Opinion at Marist College, said the White House fully understood that it could not risk a repeat of the criticism it faced after the president in 2003 stood on the deck of an aircraft carrier off the coast of San Diego under a banner that stated “Mission Accomplished.”

“They would run the risk of looking silly if they did that again,” Miringoff said. “But they will take anything that is even a small victory at this point to offset what has been a steady stream of bad news.”

The good news should give Bush some breathing room as he tries to reassert his dominance of the Republican Party and searches for a way to get a suddenly balky Republican-led Congress to follow his lead. But opinions are so hardened about a president in his sixth year, and Bush's approval ratings are so low, that not even this bit of good news from Iraq is expected to be potent enough to do much more than nudge him above the 40 percent mark.

“I'm guessing it will be very short-lived,” said Mann, adding that al-Zarqawi probably was responsible for only a small amount of the insurgent violence in Iraq. “If his death is followed by continued or even intensified violence, that will be a real downer, and that's what I expect.”

Mann said Bush may benefit more from the fact that the fledgling Iraqi government has settled on key Cabinet posts affecting the police and the military, something that was essential before there could be serious discussion of any reduction in U.S. troop levels.

Miringoff said the only movement likely in the polls will be among conservatives or Republicans who recently deserted the president to protest his immigration policies.

The White House has acknowledged that further insurgent violence can be expected. “Does this mean that happy days are here again? Of course not,” said White House press secretary Tony Snow.

But, he said, the killing of al-Zarqawi “really does mark a new day.”

Another sign of this new day at the White House is the announcement of a Camp David summit next week to assess the state of the war in Iraq.

“That may prove very helpful,” Hess said. “It shows that they are at least reaching out for some new thoughts.”

But heading into that summit, Snow continued to strike a cautious note. “We'll have to see how the public assesses this,” he said. “War can be a grueling thing. But the American people are fair-minded. We'll have to see what happens in weeks ahead.”