American commando units and naval assault forces have assembled near Yemen as the United States prepares to step up the hunt for Al Qaeda operatives in the Middle East nation, defense officials said Wednesday.

America's ambassador to Yemen, Edmund J. Hull, and military commander for the region, Gen. Tommy Franks, are negotiating with Yemeni officials on the details of a cooperative effort to capture or kill terrorist suspects there, officials said on condition of anonymity.

Talks include when and how covert missions might be attempted, who would do them -- possibly a combination of U.S and Yemeni forces -- and whether there is sufficient intelligence on the location of suspects to act.

The CIA, which has its own paramilitary units, is playing a lead role in the planning, administration officials said. CIA officials declined to comment.

Eight hundred U.S. troops, including an unknown number of special forces, have been moved to Djibouti, the tiny African nation facing Yemen, officials said. And the Marine amphibious assault ship Belleau Wood was sent to waters between Yemen and Africa in August.

Officials said Wednesday that no operation appeared imminent but that the deployments are aimed at positioning people and equipment to be ready not just for Yemen, but for any contingency around the Horn of Africa region.

The Associated Press reported over the weekend that the Bush administration was working to step up anti-terror efforts in Yemen, believed a longtime base for some suspected members of Al Qaeda as well as a sanctuary for others who fled the war in Afghanistan. It also was in Yemen that 17 American sailors were killed when the USS Cole was bombed as it refueled in 2000 in the port of Aden.

And officials say the ringleader of a suspected Al Qaeda cell uncovered in Lackawanna, N.Y., may be hiding in Yemen.

Yemen was the third place -- after the Philippines and the former Soviet republic of Georgia -- to which the Pentagon sent special forces trainers as it expanded the war on terror beyond Afghanistan this year. The 100 Green Berets in Yemen trained some 40 snipers and other troops for two months starting in May.

With training ended, the United States is plotting what it can do next in Yemen, two defense officials said. One Pentagon official portrayed planning underway for Yemen as an effort to open a new front in the military's hunt for Al Qaeda beyond the major efforts in Afghanistan and Pakistan.

Little visible progress against terrorists has been made in Yemen in recent months, although the CIA has offered intelligence and the FBI turned over a list of Al Qaeda suspects believed to be in the country.

On the southern Arabian Peninsula and across the Gulf of Aden and Red Sea from Africa, the homeland of bin Laden's father long has been a base of and transit point for terrorists.

Yemen's importance as a terrorist haven was illustrated last week, when Pakistani authorities said they had captured 10 alleged members of Al Qaeda, at least eight of them Yemenis, including suspected Sept. 11 operative Ramzi Binalshibh.

After the Sept. 11 attacks on America, Yemeni President Ali Abdullah Saleh committed his country to cooperate in the global war on terrorism. The government says it has arrested and interrogated some 100 men suspected of having links to Al Qaeda.

Secretary of Defense Donald H. Rumsfeld in the summer asked commanders to look at ways to push the hunt for Al Qaeda beyond Afghanistan, possibly through greater use of special forces commandos.

Special forces played a lead role in the war in Afghanistan and were sent to Pakistan to help find Al Qaeda figures who escaped over the border. Rumsfeld is considering giving the Special Operations Command expanded control and responsibilities in the global war on terrorism.

Rumsfeld and Joint Chiefs of Staff Chairman Gen. Richard Myers told Congress Wednesday that Special Operations Command would take over some, but not all, operations against suspected terrorists.

One advantage is that the command isn't restricted to a particular geographic area, as others are, Myers said.

"For some aspects in the war on terrorism, it's useful to have that global view," Myers said.