Gates flew from Amman, Jordan, to a command post in southern Iraq where U.S. troops are serving mainly as advisers to Iraqi forces. The advisory unit in Talil is a prototype for U.S. forces as they shift from front-line combat to support roles.
The secretary met with U.S. and Iraqi officers who have been patrolling together since July 15. He also saw the command center, a room where U.S. and Iraqi commanders meet each morning to go over coordination of patrols.
"What you are doing here is the next phase of our progress in Iraq," Gates told U.S. troops.
He told reporters he was impressed by an artillery brigade that had come to Iraq in spring thinking it would be on the front lines but quickly adapted to its advisory role. "This is a symbol of how flexible our forces are," he said.
Gates described the ground-level relationship with Iraq by saying: "Nobody's the boss or the occupier."
He also got a briefing from the No. 2 U.S. commander in Iraq, Lt. Gen. Charles Jacoby, who said overall coordination is going very well since the U.S. handed over control of the cities to Iraqi forces on June 30. Jacoby said coordination has gone particularly smoothly in Baghdad.
While in Iraq, Gates will be meeting with political leaders, including Prime Minister Nouri al-Maliki. Last week, al-Maliki met in Washington with President Barack Obama, Vice President Joe Biden, Secretary of State Hillary Rodham Clinton and senior lawmakers.
Gates is also expected to visit Iraq's restive Kurdish region, where challengers made a surprisingly strong showing in regional elections over the weekend.
Kurds were united in their hard line in disputes with Iraq's Arabs over oil-rich territory, which threaten to erupt into new violence even as the U.S. military prepares to withdraw its forces by the end of 2011.
Official results from Saturday's vote for a regional president and 111-seat parliament were not expected until later this week. But the opposition group called Gorran Kurdish for "Change" said early projections showed it had made major inroads in the parliament with a win in the city of Sulaimaniyah.
Last week, Obama pressed al-Maliki to make room in his government and security forces for all ethnic and religious groups.
U.S. officials, while praising improvement in Iraqi security forces, remain deeply concerned that al-Maliki's Shiite Muslim-dominated government has been unable or unwilling to reconcile with the country's minority Sunni Muslims and Kurds. The Sunnis had run Iraq until the U.S. ouster of Saddam Hussein in 2003 and are still smarting over their loss of power in politics, the economy and military.