DOHA, Qatar (AP) _ The United States won Qatari approval for major improvements to an air base in this Gulf nation that would play a central role if U.S. President George W. Bush ordered war against Iraq.

Upon his arrival in the Qatari capital on Wednesday night, Defense Secretary Donald H. Rumsfeld signed an agreement giving the go-ahead for several construction projects at al-Udeid air base. He said they would improve the quality of life for the 3,300 U.S. troops there and given them more “state-of-the-art capability.” He did not disclose details from the classified document.

At a news conference following the signing ceremony, Rumsfeld rebutted suggestions that the work at al-Udeid was related to American preparations for war against Iraq.

Qatar, a thumb-shaped peninsula jutting off the Gulf coast of Saudi Arabia, has emerged as a key American ally, and Rumsfeld was spending a full day Thursday touring another important facility, Camp As Sayliyah, on the outskirts of Doha, where the U.S. Central Command has set up a new command post.

Rumsfeld was meeting with Gen. Tommy Franks, the Central Command commander who has been here for a week preparing for and overseeing the conduct of an exercise, called Internal Look, that is testing the new command post’s communications links with Navy, Army, Air Force, Marine Corps and special operations commanders elsewhere in the Gulf. In the event of war in Iraq, Franks likely would run it from As Sayliyah.

The new command post was developed, and the exercise planned, before the Sept. 11 terror attacks on the United States, but the current tension with Iraq has led to speculation that Internal Look is a rehearsal for an invasion of Iraq.

Central Command officials refuse to discuss the scenarios being tested during the computer-assisted war game, which is scheduled to end early next week.

The exercise does not include troop movements.

While at Camp As Sayliyah, Rumsfeld also planned to have lunch with Franks and other senior officers, make an address to the troops at a “town hall”-style meeting, and then hold a video teleconference over secure lines with the Central Command subordinate commanders in Bahrain, Kuwait and Saudi Arabia.

Earlier this week Rumsfeld visited Eritrea, Ethiopia and Djibouti to consult on fighting terrorism in the Horn of Africa.