Future Combat Systems, an Army initiative entailing a vast combat-gear overhaul whose total cost could exceed $200 billion, “must continue to demonstrate its value for the types of irregular challenges we will face,” as well as for the full-blown land warfare for which it was designed, Mr. Gates said.

The secretary defended his order to accelerate production of heavily armored mine-resistant troop transports for use in Iraq and Afghanistan. Even at $1 million each, he said, the vehicles have proved their value by saving lives of American military personnel from improvised explosives and suicide bombings, which Mr. Gates described as “the weapon of choice for America’s most dangerous and likely adversaries.”

Addressing those who question whether the fighting in Iraq and Afghanistan has left the Army stretched to the breaking point and the nation unprepared for other conflicts, he acknowledged that “it is true that we would be hard pressed to launch a major conventional ground operation elsewhere in the world at this time.”

But he warned any adversary against thinking that the United States had dropped its guard, saying that while the Army and the Marines carried the brunt of the nation’s current combat effort, the Air Force and the Navy would be “America’s main strategic deterrent” against potential adversaries like Iran, North Korea and China. He called for careful spending to modernize and expand both of these services.

Mr. Gates’s views may not prevail beyond the end of the Bush administration, but the next president will face the same competing military priorities, while the services can be expected to renew their push for their favorite weapons programs. While disagreeing on what to do about the war in Iraq, Senators Barack Obama and John McCain have both said they would expand the number of soldiers and marines, and ensure that ground forces are properly equipped and trained for fighting insurgencies and terrorists.