The influx of Iraqis also would diminish the effect of any tightening of border controls -- a key Bush administration objective -- on the insurgency's strength.
U.S. intelligence in Iraq has frequently been wrong. However, two factors add credence to the reports of the shifting composition of Zarqawi's group: Several of his senior lieutenants have been captured by U.S. forces in recent months and some reportedly have talked extensively under interrogation.
Senior Iraqi officials reported seeing the same development.
Mowaffak Rubaie, Iraq's national security advisor and a former Shiite activist, said "there's no doubt" that once-nationalistic elements of the insurgency were drifting toward Zarqawi and his extremist Salafi sect, also known as Wahhabism, which seeks to establish a puritanical society modeled on early Islamic times.
"There's a tendency to religion-ize the insurgency," he said. "Religion is a strong motive. You're not going to find someone who's going to die for Baathists. But Salafists have a very strong message.
"If you use the Koran selectively, it could be a weapon of mass destruction."
Few Iraqis appear to share Zarqawi's goal of establishing a radical Islamic state, but small numbers of Iraqi hard-liners apparently are attracted by the effectiveness of Zarqawi's group.
"They're the best game in town, the most organized organization," said a U.S. official, who added that Zarqawi's network was also a "well-funded organization that is willing to pay people for their work" when many Iraqis, particularly police, have little or no income.
The officials noted that police in three cities, including Mosul, are not being paid. They declined to name the others.
Officials said it was not clear how dedicated these Iraqis were to the broader Al Qaeda cause, or whether they would be willing to travel outside the country to carry out terrorist attacks in Arab or Western nations.
Zarqawi escaped capture in February near the city of Ramadi, authorities say. He fled on foot as coalition forces at a checkpoint intercepted a truck containing a laptop and documents. Coalition forces since have killed or captured several of his lieutenants. The latest such incident was announced Sept. 9, when a U.S. military official said a high-level aide had been killed in western Iraq.
But the U.S. officials who are familiar with intelligence on Zarqawi's group said the organization had proved remarkably resilient and was organized to withstand losses of key leaders, including Zarqawi.
