BAGHDAD — Defense Secretary Gates said today that although no additional American combat brigades are to withdraw from Iraq this year, he expects the American combat role to keep shrinking.

“We are clearly in a mission transition,” he told reporters on an overnight flight here from Washington.

American troops will increasingly play a backup role, Mr. Gates said, as Iraqi security forces take on more of the responsibility for fighting an insurgency that has lost much of its power and influence over the past year.

“The areas in which we are seriously engaged (in fighting) will, I think, continue to narrow,” Mr. Gates said.

The No. 2 American commander at Iraq, Lieutenant General Lloyd Austin, told reporters later at the main American military headquarters outside Baghdad that he remains optimistic that the trend of improving security will continue.

Key measures of security have improved about 80 percent over one year ago; while “there is a degree of fragility” to the situation, he said, it is “somewhat less” fragile than just a few months ago.

The biggest uncertainty at the moment, General Austin said, is the central government’s inability thus far to pass the legislation needed to hold provincial elections across the country before the end of the year. Mr. Gates is meeting with Iraqi Prime Minister Maliki later today.

General Austin also said the al-Qaida in Iraq remains a source of concern.

“Al-Qaida is in disarray but they have not yet been defeated,” he said.

Iraq currently has primary responsibility for security in 11 of its 18 provinces. It regained responsibility for Anbar province, at one time the stronghold of the Sunni insurgency, a few weeks ago.

In the interview, Mr. Gates said he is focusing heavily now on expanding the use and effectiveness of intelligence and surveillance programs that have played an important part in eroding the insurgency in Iraq.

It is Mr. Gates’ eighth trip to Iraq since becoming defense secretary in December 2006.

Sandstorms prevented Mr. Gates’ aircraft from stopping as planned at Camp Speicher, near the northern city of Tikrit, to receive a briefing on a once-secret program, known as Task Force Odin. The program has innovatively linked a variety of surveillance and reconnaissance aircraft — drones as well as manned planes — with new sensor technologies to hunt down insurgent cells. Those assets also are linked to attack helicopters and other planes capable of striking at discrete targets on short notice, day and night. One of the keys has been expanding the availability of full-motion video cameras aboard aircraft that can transmit live images to other aircraft and to ground stations, enabling quick action.

“We have a lot more plans under way” for expanding that program, Mr. Gates said.

Mr. Gates told Congress last week that he wants to replicate Task Force Odin in Afghanistan as soon as possible.

Lieutenant General Richard Zahner, the deputy undersecretary of defense for intelligence, who was traveling with Mr. Gates, told reporters during a stop at Incirlik air base at Turkey today that he is pushing a plan to expand the uses of similar intelligence and surveillance operations in both Iraq and Afghanistan.

General Zahner said, for example, that the number of 24-hour-a-day “orbits” — nonstop air patrols over a particular area using remotely piloted Predators and other drones, teamed with specially equipped manned intelligence aircraft — in Iraq and Afghanistan combined has climbed from 12 in June 2007 to 27 today. It is due to rise to 28 next month and he hopes to push it to about 55 by the end of 2009.

The press secretary to Mr. Gates, Geoff Morrell, said Congress has been asked to provide $1.2 billion for the expansion of such programs in Afghanistan, where the insurgency has become more active and more deadly.

Mr. Gates plans to attend a ceremony tomorrow at Baghdad where Lieutenant General Ray Odierno will take over for General David Petraeus as the top American commander in Iraq. General Odierno was the No. 2 commander when he left Iraq in February. General Petraeus is set to become commander of U.S. Central Command, where he will have responsibility for American military involvement throughout the Middle East and Central Asia.

In the in-flight interview, Mr Gates offered high praise for General Petraeus while also expressing confidence in General Odierno.

“He’s played a historic role,” Mr. Gates said of General Petraeus, who arrived at Baghdad as the top commander in February 2007 and implemented a revised counterinsurgency strategy, aided by the deployment of five additional Army brigades and other factors, that resulted in a drastic reduction in violence.

“General Petraeus is clearly the hero of the hour,” Mr. Gates said.

Mr. Gates, like his predecessor at the Pentagon, Donald H. Rumsfeld, has made regular visits to Iraq to consult with American commanders and senior Iraqi government officials as well as to meet privately with troops.

Mr. Gates has not been here, however, since February. That is an unusually long stretch between visits, reflecting in part the calmer conditions that have prevailed this year as violence eased and five Army brigades that President Bush had sent as reinforcements in 2007 finished their tours and went home.

Among the tough issues Mr. Gates faces before the Bush administration ends in January is completing a security agreement with Iraq that would provide a legal basis for American troops to remain in the country after a U.N. mandate expires in December.

Talks were said to be near agreement in August but have since reached a stalemate.