They are the secret warriors in America's hidden war: CIA and Special Operations forces who ride into battle on pickup trucks, dune buggies and helicopters.

As the U.S.-led campaign evolves from a seen-on-TV bombing campaign to a cave-by-cave hunt for Al Qaeda and Taliban holdouts, covert U.S. agents and troops are increasingly fighting the key battles.

But the Pentagon keeps details of this war secret. Only rarely — as with a Special Forces raid on Taliban forces this week — is a some light shed on their operations. Even conventional U.S. forces also on the ground in Afghanistan are kept in the dark.

Troops from conventional units stationed at the airport here refer to the special forces as "the alphabet guys" — bearded warriors hidden behind sunglasses. Official military statements rarely mention them.

In Kandahar, Afghan provincial official Khalid Pashtun half-apologized this week for his gunmen's threats to shoot news photographers — at the behest, the gunmen said, of camera-hostile Special Forces whom the reporters were trailing.

"We need them more than we need you," Pashtun told journalists. "What can we do? Which would you choose?"

No U.S. soldier relayed the threat directly to any of the reporters and it was impossible to tell whether Pashtun embellished the instructions. However, the incident shows the close contact between Special Forces and Afghan allies and the lengths to which both go to keep operations secret.

Covert U.S. forces, including the Army Green Berets or Special Forces, are known as Special Operations forces and drawn from all three armed services. They are spearheading operations against what Afghan leaders say are hundreds of fugitive Taliban and Al Qaeda.

Army Special Forces led one of the largest such operations on Wednesday, flying by helicopter to raid what the Pentagon says appeared to be Taliban military compounds in the north. The Pentagon reported about 15 enemy fighters killed and 27 captured. One American soldier was wounded.

Villagers, however, claimed U.S. forces bombed their town hall and clinic, and killed and arrested innocent people and men loyal to Afghanistan's U.S.-backed interim leader, Hamid Karzai.

But the Army called the raid a success — one of many, it said, for the in-and-out Special Forces.

"I think it's safe to say this war has been anything but conventional," Army spokesman Capt. Tony Rivers said at the Kandahar base Saturday.

Speaking of the covert forces, Rivers said, "In my opinion, they're the most significant reason for the success we've had in this war."

That success, however, has not been complete. Usama bin Laden, the prime suspect in the Sept. 11 attacks, remains at large, as does Taliban leader Mullah Mohammed Omar.

U.S. Gen. Tommy Franks, commander of the U.S.-led Afghan campaign, said Saturday that sending more conventional troops would not have increased the military's chances of catching bin Laden.

"The tactics in this operation were just the right tactics," Franks said. He invoked the bogged-down 1980s Soviet campaign in Afghanistan. "One does not want to commit mistakes that have been committed by other people in the past."

Special Operations forces are believed to number at least in the hundreds in Afghanistan. No U.S. official will give a firm number, citing security. These commandos — whose troops are hand-picked, better trained and equipped than ordinary infantrymen — were created for just the kind of fast, small-scale operations under way in Afghanistan.

CIA paramilitaries, working under the agency's Special Activities Division, operate alongside U.S. military, Afghan allied forces, or alone.

Franks and others have emphasized intelligence over blunt force in the campaign. Some CIA contacts no doubt date back to association with Afghan guerrilla fighters during the war against Soviet invaders. The United States and its allies secretly armed and trained Afghan resistance fighters.

But by their nature, little information on their work is reaching the public. For example, the briefings at the U.S. base at Kandahar airport have to do mostly with efforts to secure and run the base — the trials of getting a working water system in place are a running serial.

Covert forces, meanwhile, slip in and out of the Kandahar base without fanfare, dressed in black fleece jackets and khakis, weapons strapped to their legs or slung on their backs.

Some have beards, even Afghan shawls, pulling them up over their face when cameras come near. Pale skin and big builds — in contrast to scrawny, hungry Afghan fighters — often give them away in the field.

At Kandahar, a beat-up hangar on a far end of a runway holds their aircraft. A futuristic-looking buggy in non-reflective black carries some out of the gates.

The men themselves go to lengths to protect their identities. Reporters have repeatedly accused Special Operations forces of setting local gunmen against them when journalists trail the operatives or the Afghan officials they often accompany.

"Don't worry, they won't kill you," one Special Forces agent told an AP photographer in December, as tribal fighters near the mountains of Tora Bora shook down a group of photojournalists for their cameras and other gear. The Pentagon has refused to comment on the incident.

Some interactions are cordial, when limited to banter.

Americans often learn of covert operations only when something goes wrong — as the crash this week of two unmanned Predator drones. The U.S. surveillance planes have seen heavy use in Afghanistan, including by the CIA, which has dispatched some armed with missiles on their wings to attack Taliban and Al Qaeda targets.

The crash of a Marine resupply flight last week cast light on what appears to be a center of special operations at central Afghanistan's Bagram airfield. Two Marines died.

Military officials at Bagram were tightlipped about just who was being resupplied.

"Was it a Special Forces group?" a reporter asked.

"You can draw your own conclusions," a military spokesman replied.