The Western diplomat said that even if most of the bodyguards remained Blackwater veterans, there would be dramatic changes in their rules of engagement. One former Marine Corps colonel who worked closely with Blackwater summed up the previous rules: “No compassion for the locals who had to use the roads with the Blackwater vehicles or convoys, shoot if in doubt and keep driving, etc.”

The new rules of engagement, the diplomat said, would require staff members to behave less aggressively. They had already started to take effect, he added, with Blackwater escorts ordered to negotiate traffic courteously.

After Iraq refused to renew Blackwater’s contract, the State Department awarded it to Triple Canopy, one of two other firms, including DynCorp, already doing some State Department security contracting in Iraq. The five-year State Department contract, awarded March 31, is worth $977 million and goes into effect May 7. That amount represents a large proportion of Blackwater’s previous worldwide business.

American officials said replacing Blackwater from scratch in just over a month would be difficult. The firm maintains a force of 600 armed men based in Baghdad’s Green Zone to protect embassy and other United States government civilian employees. Their work requires security clearances when they accompany diplomats on sensitive missions, involving lengthy background checks. It is particularly difficult for non-Americans to get such clearances.

Blackwater also maintains a quick reaction force, and has a civilian air wing with helicopters, surveillance drones and other aircraft. The contract for their air operations remains in force, expiring in September.

Although Triple Canopy is an American company, most of its Iraq-based employees are former members of the military from countries with low wage scales, like Peru and El Salvador, with a much lower level of training or expertise than Western employees, and little likelihood of getting security clearances.

Many American diplomats have defended Blackwater. At least six American State Department employees have been killed since the occupation of Iraq, and Ms. Tyrell said that 27 Blackwater personnel members were killed defending their charges. “A certain number of our people are here today because Blackwater guards have been killed protecting them,” said an official familiar with security arrangements for American diplomats, who did not want to be identified because he was not authorized to speak to the news media.

The Iraqis now seem prepared to accept the prospect that many or even most of the former Blackwater employees will remain on the job as Triple Canopy employees. “It doesn’t matter who they are, what their names are, or what uniform they wear,” said Brig. Gen. Abdul-Karim Khalaf, spokesman for the Iraqi Interior Ministry, “as long as they are subject to Iraqi law and their company follows Iraqi laws.”