Through a pair of binoculars, Staff Sgt. Jerry Pat Moss recalled, the four Iraqi men on the horizon looked out of place. They maneuvered like soldiers, running a few steps and then dropping to their stomachs and waiting, before continuing on their way. In bluejeans and button-down shirts, they could hardly pass for local peasants, who wear long robes.

Moss, who spotted the men today while on a routine patrol near the site of a recent ambush of a Marine fuel convoy, decided he wanted a closer look. So he plowed across the marshland in his Amtrac amphibious assault vehicle. When he got close, he said, he ordered the four men to the ground to be searched and found military identification cards in their pockets.

After sporadic clashes with Iraqi army units in the southern part of the country, the Marines are fighting what Lt. Col. Christopher Conlin called "a new phase in the war, against a different kind of enemy." He was referring to Saddam's Fedayeen, a national militia loyal to the Iraqi government.

Moving among local populations, the Fedayeen are more difficult to identify, and therefore harder to target, than uniformed military forces.

The men captured today "clearly fit the Fedayeen profile," said Conlin, who commands the 1st Battalion, 7th Marine Regiment.

In addition to the identification cards, the prisoners were found with small amounts of cash, including some U.S. currency, said a Marine who performed the initial search. They were placed in a makeshift pen with gravel walls. For several hours they crouched in the sun, with their hands bound and their faces covered with canvas bags. They were fed and given water.

A team of interpreters and interrogation specialists, including a few civilians of Iraqi descent who speak Arabic and are assisting the Marines in gathering information from the local population, questioned the captives. A Marine who observed the interrogations said the prisoners were pressed on the location and condition of U.S. prisoners of war.

"Anytime you can get into the mind of the enemy, it's valuable," said Gunnery Sgt. Aaron Hall, part of the intelligence team that oversaw the interrogations. "It has given us some insight, for instance, into why we may not have seen as many soldiers surrendering as some people thought."

Many of the more than 80 prisoners the battalion has taken during the conflict, Hall said, had been convinced by Saddam's Fedayeen that they would be killed if captured by U.S. forces. "And not just shot dead -- tortured first," he added.

Guided by evidence obtained from the prisoners today, Conlin and some of his company commanders took to a Huey helicopter to search the area for militia camps. None was found. If a camp had been located, it could have been targeted and destroyed within hours, he said.

The Fedayeen specialize in small-scale but potentially deadly ambushes, such as an attack Sunday on Marine logistics specialists in Nasiriyah.

"In the south we fought their regular army, which we could find and destroy," Conlin said, recalling the Marines' first experiences a week ago and more than 120 miles away. "Here we are fighting against a group that employs mostly guerrilla tactics. It has some of the feeling of the conflict in Afghanistan, because we are having to fight both conventional and unconventional forces."

This phase in the conflict poses a particular challenge to the Marines, Conlin said, because it can be so difficult to distinguish friend from foe. "The people waving at you in the streets one day could be shooting at you that night," he said. "And we have prepared [troops] to deal appropriately with both situations."

Saddam's Fedayeen are political militiamen tied to President Saddam Hussein's ruling Baath Party, said the battalion's intelligence officer, Kohtara Terahira. "One of their missions is to overwatch the regular army to make sure they stay loyal to the Iraqi government," he said. "The other is to mobilize the local population."

Because most Fedayeen are armed only with rifles and other small arms, they mainly attack soft targets, such as noncombat units, said Terahira. These include units providing logistical support for the Marines pushing north toward Baghdad. To help keep the support troops safe, Terahira said, the battalion has put infantry forces alongside them in areas that have not yet been secured.

Because the militia's movements are more difficult to track than those of regular army units, the Marines are increasingly relying on intelligence gleaned from prisoners. "We try to find information on the location of hostile forces, or plans for future attacks," Terahira said. "Some enemy prisoners of war can be useful in giving us a better picture of the threat."