A man described by police as an Asian wearing a trenchcoat on Thursday night stole a briefcase stuffed with sensitive documents from the Philippine government's chief investigator, who brought the records to the United States from Manila in an effort to recoup the wealth of deposed President Ferdinand Marcos.

The investigator, Jovito Salonga, was seated with his wife and daughter in the waiting area of a midtown Manhattan restaurant when Salonga's briefcase -- containing the documents, plane tickets, passport and $3,000 in cash and traveler's checks -- was snatched.

The thief also took a Gucci handbag with $2,000 in traveler's checks and $1,400 in cash belonging to Salonga's wife, police said.

It was unclear yesterday whether the theft was related to Salonga's investigation into Marcos' financial holdings. Police Lt. James Robert said "this incident is being treated as a diplomatic incident," but he added that "this type of incident is not uncommon in the midtown area."

Sources close to Salonga suggested that the crime may have been coincidental, or at worse may have been committed by a Filipino who feared his name may appear in the documents. These sources sought to play down speculation that the theft was orchestrated by Marcos supporters.

The incident occurred shortly before 9 p.m. Thursday when, according to the police report, the thief approached the Salonga party and pointed to five $1 bills lying on the floor. The daughter, Victoria, stooped to pick them up while her parents watched, and when she straightened up the briefcase, handbag and thief were gone.