WASHINGTON - The U.S. military's top officer acknowledged yesterday that for all the importance of preventing Afghanistan from again harboring al-Qaeda terrorists, Washington's first priority was Iraq.

"In Afghanistan, we do what we can," said Adm. Mike Mullen, chairman of the Joint Chiefs of Staff. "In Iraq, we do what we must."

His statement to the House Armed Services Committee prompted some Democrats to say it showed what they have argued for years: that the Bush administration has become so bogged down in Iraq that it cannot make more effort in Afghanistan.

Mullen, testifying with Defense Secretary Robert M. Gates on the effort to stabilize Afghanistan, said that war was, "by design and necessity, an economy-of-force operation. There is no getting around that."

The United States has about 166,000 troops in Iraq and about 25,000 in Afghanistan.

Asked by committee members about the long-futile effort to find al-Qaeda leader Osama bin Laden, Mullen and Gates said the hunt was a high priority. But they did not offer specifics about what U.S. forces were doing to track him.

Gates and other officials have said al-Qaeda and Taliban fighters were finding refuge and operating training camps on the Pakistan side of the border, then slipping into Afghanistan. Gates noted yesterday that the United States would not send conventional military forces into Pakistan to deal with the problem, but added, "That's the area we do need to be concerned about - al-Qaeda training and reconstituting itself."

The first option for dealing with that, Gates said, is encouraging the Pakistanis to act more aggressively on their own and, second, for U.S. forces to work together with the Pakistani military.

Gates said the security and other gains in Afghanistan were fragile. "There needs to be more effective coordination of assistance to the government of Afghanistan," Gates told the committee. "A strong civilian representative is needed to coordinate all nations and key international organizations on the ground.

"We and others have worked with the Karzai government to identify a suitable candidate. I'm hopeful this exhaustive search will be completed soon."