WASHINGTON (AP) _ With the principal goal of Operation Just Cause met - the capture of Manuel Antonio Noriega - the U.S. focus is on repairing Panama's basic services and utilities destroyed or disrupted in the invasion.

Call the troops landing in Panama ''nation-building forces,'' the Pentagon says.

''Civil affairs personnel ... people who provide police service and assistance to utilities and that kind of thing,'' Pentagon spokesman Pete Williams told reporters Thursday in describing the specialists sent to Panama.

The number of U.S. servicemen in Panama stands at about 25,500, the same as it was shortly after the invasion, as combat troops are withdrawn and replaced by military police and civil affairs specialists, Williams said.

''So what you have is a change - even though in some cases the numbers may stay roughly the same, you have a change in the complexion of the force,'' Williams said.

Gen. Colin Powell, the chairman of the Joint Chiefs of Staff, arrived in Panama on Thursday to meet with Gen. Maxwell Thurman of the U.S. Southern Command and work out a timetable for withdrawal of the troops.

Prior to the invasion on Dec. 20, about 12,000 U.S. troops were stationed in Panama to guard the canal under the terms of a treaty under which the United States is to turn the waterway over to Panama in the year 1999.

The civil affairs specialists include active and reserve, officers and enlisted men, bankers and garbage collectors. To date, about 140 reserves from around the country and about 110 active-duty specialists from the 96th Battalion at Fort Bragg, N.C., have been sent to Panama. About 25 of them arrived during the first 48 hours after the invasion.

Their purpose, according to the Pentagon, is to help the Panamanians repair and restore basic public services such as telephone, water and electricity. A group of combat engineers is expected later with bulldozers to destroy what is left of the Commandancia, the headquarters of the Panamanian Defense Forces, said Pentagon spokesman Col. Miguel E. Monteverde.

The specialists are similar to those who were sent to Japan and Germany following World War II.

''They are experts in government and municipal services,'' Monteverde said.

During the briefing, Williams said fighting had all but ceased in Panama.

In other developments, the Pentagon spokesman said one of Noriega's bodyguards overheard U.S. servicemen discussing the invasion hours before it occurred, but it was unclear whether the incident enabled the ousted Panamanian leader to evade the Americans.

''There is some evidence that some officials may have had some advance thought that this operation was about to happen. But there isn't a lot of evidence that actions were taken as a result of that,'' Williams said.

''A bodyguard, during a debriefing interview, said that two U.S. soldiers had been overheard discussing their positions for H-hour. And that supposedly happened at 10 p.m., three hours before the attack was to begin,'' said Williams. ''I have no other details.''

Noriega is believed to have escaped from one of his residences minutes before a U.S. commando unit arrived just after midnight Dec. 20, and fled from house to house in Panama City in the days thereafter, according to military officials. Noriega found refuge in the Vatican Embassy on Dec. 24 and turned himself over to U.S. officials Wednesday.