"There is no immediate alterative to Zarqawi," the senior Iraqi intelligence official said. "There will be a vacuum of leadership. His close circle, his organization, will not agree on one of them to succeed him. There is the prospect for division in this group."  A similar thing happened among the senior leaders of the Palestinian terrorists clustered around Abu Nidal in the 1980's, when assassinations ignited a violent struggle, according to Mr. Hoffman, the RAND Corporation analyst.  "This is the best way to undermine a terrorist group," he added. "Information that sows internal discord and disloyalty has a radiating effect in the organization. That could set in motion the unraveling of Al Qaeda."  Maj. Gen. William Caldwell, a spokesman for American forces in Iraq, said the likely successor to Mr. Zarqawi was a person known only by his nom de guerre, Abu al-Masri. Al Masri means "the Egyptian."  In a statement posted on a jihadi Web site, a writer claiming to be the deputy emir of Al Qaeda in Mesopotamia, Abu Abdul Rahman al-Iraqi, vowed to carry on with "the same plan that Abu Musab al-Zarqawi drew up."  "We pledge to God to continue raising his way in the Land Between the Rivers, or die," the statement said. Mesopotamia means "the Land Between the Rivers."  In recent months, American officials said they had decimated Al Qaeda in Mesopotamia. At news conferences, they flashed photo after photo of people who they said were killed or captured leaders. Despite these statements, the organization continued to mount extraordinarily lethal attacks. That suggested that Al Qaeda was rapidly replenishing its ranks; it could do so again.  In any event, the fruits of Mr. Zarqawi's labors may outlive him. Filled with hatred for Iraq's Shiite majority, whom his group often referred to scornfully as "converters," Mr. Zarqawi killed thousands of them, mostly civilians struck by one of the suicide bombers he dispatched to markets, street corners and police recruiting stations.  The most spectacular and overtly sectarian attack came on Feb. 22, when bombers destroyed Al Askariya, a golden-domed mosque revered by Shiites. That set off a wave of Shiite-on-Sunni violence  precisely what Mr. Zarqawi had hoped for  and a violent backlash by Sunni gunmen.  On the day of Mr. Zarqawi's death, Iraq stood at the brink of all-out civil war, and no one did more than he did to bring that about.  Mowaffak al-Rubaie, the national security adviser, said he hoped there was still time to slow the slide into sectarian bloodletting.  "There is a fracture between the two communities," Mr. Rubaie said. "His work over the last three years has not gone in vain."
While Abu Musab al-Zarqawi's death could erode his group's ability to carry out attacks, the insurgency he helped ignite will go on without him, according to officials.