Washington ? As the White House eagerly highlights the departure of U.S. combat troops from Iraq, the small army of American diplomats left behind is embarking on a long and perilous path to keeping the volatile country from slipping back to the brink of civil war.

Among the challenges are helping Iraq’s deeply divided politicians form a new government; refereeing long-simmering Arab-Kurd territorial disputes; advising on attracting foreign investment; pushing for improved government services; and fleshing out a blueprint for future U.S.-Iraqi relations.

President Barack Obama also is banking on the diplomats — about 300, protected by as many as 7,000 private security contractors — to assume the duties of the U.S. military. That includes protecting U.S. personnel from attack and managing the training of Iraqi police, starting in October 2011.

The Iraq insurgency, which began shortly after U.S. troops toppled Baghdad in April 2003, is why the U.S. only now is entering the post-combat phase of stabilizing Iraq. Originally, the U.S. thought Iraq would be peaceful within months of the invasion, allowing for a short-lived occupation and the relatively quick emergence of a viable government.

Although the insurgency has been reduced to what one analyst terms a “lethal nuisance,” it will complicate the State Department’s mission and test Iraq’s security forces.

Much is at stake as the department negotiates with the Pentagon over acquiring enough Black Hawk helicopters, bomb-resistant vehicles and other heavy gear to outfit its own protection force in Iraq.

“Regardless of the reasons for going to war, everything now depends on a successful transition to an effective and unified Iraqi government and Iraqi security forces that can bring both security and stability to the average Iraqi,” says Anthony Cordesman of the Center for Strategic and International Studies. In his view that transition will take five years to 10 years.

The question is whether progress will be interrupted or reversed once American combat power is gone.

The U.S. will have 50,000 troops in Iraq when the combat mission officially ends Aug. 31; they are scheduled to draw down to zero by Dec. 31, 2011. Until then, they will advise and train Iraqi security forces, and provide security and transport for the diplomats.

Gen. Ray Odierno, the top U.S. commander in Iraq, said in an interview to be broadcast today on CNN’s “State of the Union” that he believes Iraq’s security forces have matured to the point where they will be ready to shoulder enough of the burden to permit the remaining 50,000 U.S. soldiers to go home at the end of next year.

“My assessment today is they — they will be,” Odierno said, according to an excerpt of the interview released Saturday by CNN.

“We continue to see development in planning, in their ability to conduct operations,” he added. “We continue to see political development, economic development and all of these combined together will start to create an atmosphere that creates better security.”

Once the U.S. troops are gone, the State Department will be responsible for the security of its personnel.

Obama administration officials say the diplomats are well prepared for what the State Department expects to be a three- to five-year transition to a “normal” U.S.-Iraqi relationship.