COMBAT IN PANAMA : U.S. Troops Now Facing Uncertain Phase of Mission : Military: Americans must contend with elusive remnants of Noriega’s best-trained troops and roaming bands of youths.

A day after subduing most organized resistance mounted by the Panama Defense Forces against their invasion, U.S. soldiers confronted one of the most shadowy and uncertain phases of their mission Thursday.

As the American troops moved to restore order to a Panama City turned lawless, they faced the elusive remnants of some of ex-strongman Manuel A. Noriega’s best-trained troops, as well as some of his most unpredictable, who are shooting from rooftops, entering houses and roaming the streets in disorganized bands.

Members of Noriega’s special operations forces, many wearing black masks, are sniping from rooftop perches, Pentagon officials said. Meanwhile, a rabble from the so-called Dignity Battalion, some armed with AK-47 rifles and rocket-propelled grenade launchers, threaten U.S. troops from the cover of buildings. The Dignity Battalion consists of young, paramilitary Noriega loyalists recruited from poor neighborhoods.

“We wanted to take down the PDF; we’ve pretty effectively done that,” said Army Lt. Gen. Thomas W. Kelly, director of the military’s Joint Chiefs of Staff. “We wanted to restore law and order. We’re doing that today (Thursday).”

However, Pentagon planners admitted that they still fear that such pro-Noriega forces as Battalion 2000, which Wednesday fled its base north of Panama City, might have retreated into Panama’s dense jungles to regroup.

“We carry them as a possible future problem,” said Kelly of the force. Battalion 2000, which has 500 to 800 men, was established by Noriega in 1983 to protect the Panama Canal when, under the terms of the Panama Canal Treaties with the United States, the waterway is turned over to Panama in the year 2000. The battalion was helpful to Noriega during the October coup attempt against him, but Kelly said Thursday that it is not clear whether it remains intact.

Units from the 7th Infantry Division, based in Ft. Ord, Calif., and a brigade of more than 300 military police from Ft. Bragg, N.C., arrived in Panama on Thursday and joined Army Rangers and paratroopers who already had begun to patrol Panama City’s streets. The additions brought the total U.S. force to 22,500.

Kelly said that the 16th Military Police Brigade will allow local commanders to establish communications that will permit the U.S. forces to perform “some police functions in Panama City insofar as rounding people up and disarming them are concerned.”

Infantryman from the 82nd Airborne, riding in high-tech trucks called “Hummers,” rushed past rooftop snipers at the Marriott Hotel, where 29 American and 35 foreign nationals were pinned down, and evacuated the civilians Thursday morning. U.S. soldiers combed a second hotel for possible hostages.

At the same time, the Americans salvaged what Kelly described as “a large cache” of PDF documents from the burned-out remains of Noriega’s headquarters. The documents were to be combed by military intelligence analysts and whisked to Justice Department officials for use as evidence in the prosecution of Noriega on drug-trafficking charges.

Meanwhile, other Army Rangers, as well as special operations forces, scoured the countryside to bring in Noriega--a task that Kelly called “one of our top priorities.”

Secretary of Defense Dick Cheney, in an interview, said that the task of mopping up “would be a little easier if Noriega wasn’t dashing around the country.”

Rear Adm. Ted Sheafer, the Joint Staff’s intelligence chief, said Pentagon intelligence analysts believe that Noriega remains in Panama. But he added that there have been “innumerable reports” of sightings, including some that place him in Mexico, the Dominican Republic and Colombia.

Fearing that Noriega might try to flee to Nicaragua or Cuba, U.S. soldiers kept well-armed surveillance on those nations’ embassies in Panama City, Pentagon officials said. They denied reports that the embassies were surrounded by tanks.

In preparation for an intensified manhunt, Pentagon officials said that the operation’s next step would be the deployment of some troops close to Panama’s northern border with Costa Rica. That section of Panama is a traditional stronghold for the deposed dictator.

While many of the PDF’s 7,300-man regular force appears to have disappeared into Panama’s civilian population or into the jungles, American forces by Thursday morning had rounded up 1,500 prisoners, Pentagon officials said.

They estimated that by Thursday morning, 59 Panamanian soldiers had been killed in the fighting and 66 wounded. They said they had no estimates of civilian casualties, although Panamanian hospital officials estimated that hundreds of civilians were treated for wounds.

By Thursday night, 21 U.S. servicemen had died in Panama and 208 were wounded. Another four were missing.

As U.S. forces began the task of interrogating prisoners, Noriega’s brother-in-law, an officer in the PDF, contacted U.S. forces and offered to surrender along with 15 fellow soldiers, according to Kelly.

U.S. soldiers also faced the delicate task of distinguishing Panamanian civilians from straggling Panamanian troops intent on ambush.

Along with night-time parachute operations, which the 82nd Airborne conducted early Wednesday morning, urban warfare “is one of the most difficult and dangerous forms of maneuver there is,” said Lt. Col. Bob Killebrew, a Pentagon official who until two months ago commanded the 1st Battalion of the 82nd Airborne’s 504th Parachute Infantry Regiment, now in Panama.