At the same time, helicopter-borne special forces teams are poised for what is likely to be a prominent role in the next phase of the war.

Air war planners have selected 5,000-pound "bunker-buster" bombs for use against underground bunkers used by Taliban leaders to coordinate military operations, three senior defense officials said. The officials, who discussed the matter on condition they not be identified, said they did not know whether the bunker strikes had been carried out as planned Tuesday and Wednesday.

The GBU-28, whose inventory and performance characteristics are classified secret, was developed for the Gulf War to strike deeply buried targets. It was used on Feb. 27, 1991, against a bunker complex in Iraq; two years ago a version with improved guidance systems was put into production.

The officials said U.S. warplanes also would begin dropping cluster munitions _ bombs that dispense smaller bomblets _ for use against moving and stationary land targets such as armored vehicles and troop convoys.

Special forces "will have a significant role in all the areas they are trained to perform in," said Army Col. Bill Darley, a spokesman for U.S. Special Operations Command.

The next phase of the U.S. strikes could include raids by small groups of Army Special Forces soldiers ferried in by low-flying helicopters to rout out terrorist or Taliban leaders, military analysts say. The forces would likely use Black Hawk helicopters, which can carry up to 14 commandos and their gear and have equipment allowing them to fly low and fast at night or in bad weather.

Small teams of British and U.S. special reconnaissance teams were already inside Afghanistan before this week's airstrikes began. But the next deployment is expected to be much larger now that the strikes have a paved the way freer movement of troops.

Aerial bombing will continue as well, Secretary of State Colin Powell said Wednesday.

"There are still targets that are being examined for restrike and there are additional targets" that military commanders are looking at, Powell said on ABC's "Good Morning America."

Meantime, the air campaign continued for a fourth day Wednesday when jets dropped three bombs near the airport in the southern city of Kandahar in the second straight morning of daylight raids, Taliban sources said.

On Tuesday, the Taliban also reported strikes around Kandahar, the ruling militia's headquarters, and the northwestern city of Herat. Anti-aircraft fire and the roar of jets could be heard in the capital, Kabul, at night.

Pentagon officials said the Taliban's meager air defenses had largely been wiped out.

"Essentially we have air supremacy over Afghanistan now," Air Force Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said at a joint news conference with Defense Secretary Donald H. Rumsfeld.

That was disputed by the Taliban envoy to Pakistan, Abdul Salam Zaeef.

The "claim that they destroyed the defense capability of the Islamic Emirate of Afghanistan is not true," he said Wednesday. "American planes are flying very high, and the defense system that we have, they are not in the range of what we have."

Zaeef also said the fighters of Northern Alliance had failed to make advances against Taliban forces despite the U.S.-led air strikes. Rebels trying to topple the Taliban said they were being bolstered by the American-led air campaign.

The aircraft carrier USS Kitty Hawk was headed to the region without its usual number of airplanes aboard, allowing it to be used as a floating base for special forces operations.

"I think you'll probably see helicopters inserting special forces personnel and extracting them," said Sen. John McCain, R-Ariz., a former Navy pilot. "The scenario of an all-out ground invasion is just not in the cards ... but you probably have to go in on the ground to make sure that the training camps and other terrorist networks are eliminated, and that means the risk of American lives."

At Tuesday's briefing, Myers and Rumsfeld showed before-and-after slides of a devastated Afghan terrorist training camp, an anti-aircraft site and an airfield. The later pictures showed most of the training camp had been reduced to rubble, the anti-aircraft site was a smoking crater and the airfield runway was pocked by bomb blasts.

By Tuesday air mission planners were moving on to what Rumsfeld called "emerging targets" _ any target of value that popped into view, whether it be a Taliban troop convoy or an al-Qaida leader, including prime terror suspect Osama bin Laden.

Bomber crews said several planes involved in later rounds of strikes had their targets changed after they had taken off.

The strikes against the Taliban could make it easier for outmatched rebel forces, who control 5 percent to 10 percent of northern Afghanistan, to attempt removal of the ruling militia.