Alleged Spy Called Brilliant, Erratic : Espionage: An FBI agent testifies that the ex-soldier admitted selling NATO secrets. A search for some of the classified documents is under way.

An ex-Army sergeant charged in one of the most significant espionage schemes ever uncovered appeared in court in Tampa, Fla., on Friday, while federal agents there searched three sites for top-secret documents that the former soldier allegedly hoped to sell to foreign agents.

An FBI investigator described the ex-GI, Roderick James Ramsay, as a brilliant but erratic man who had admitted being paid thousands of dollars for passing to East Bloc agents top-secret NATO documents detailing the nuclear defense of Europe.

The government testimony suggested that Ramsay, 28, now an unemployed taxi driver, was among the most important figures in an espionage ring that the chief federal investigator described Friday as “one of the most serious breaches ever.”

According to U.S. and West German officials, Ramsay, working in collaboration with an Army superior convicted of treason earlier this week, handed over to the KGB information that would have gravely endangered the capability of the West to defend itself in the event of a Soviet attack.

FBI agent Joe Navarro, a specialist in counterintelligence and espionage, said the information turned over to the East Bloc agents by Ramsay “in effect neutralized” the North Atlantic Treaty Organization, because Warsaw Pact nations “knew all our plans.”

“This is a significant case from the point of view of damage to U.S. security interests,” said Justice Department spokesman Doug Tillet. “It involves an extensive amount of information provided to the Soviet intelligence service through Eastern Europe surrogates.”

Officials said that Ramsay, whose court hearing was continued until next week, had been cooperating with authorities. The ex-sergeant, represented by a court-appointed attorney, did not make a statement during the 90-minute proceedings. His mother, Dorothy Ramsay, cried as deputy marshals took Ramsay from the courtroom.

Ramsay is charged with conspiracy to gather or deliver defense information to a foreign government. The charge carries a maximum penalty of life imprisonment.

Federal officials described Ramsay as a junior but important partner of then-Army Sgt. Clyde Lee Conrad, who was convicted of treason in a West German court earlier this week. The two men had worked together in the mid-1980s as archive clerks with top-secret clearance at U.S. Army 8th Infantry Headquarters in West Germany.

One law enforcement official said the government feared that what had been learned so far about the spy ring represented “just the tip of the iceberg” in a case that may have involved half a dozen soldiers and a wide range of national security secrets. He said also that the operation may have continued long after the two men left the Army.

In the Tampa hearing Friday, Navarro said that Ramsay “had the ability to recall minute details, facts and figures--some from documents he hadn’t seen in five or six years.” Ramsay also hid top-secret documents in his mother’s residence in Tampa and had planned to sell them in the future, the federal agent told U.S. Magistrate Elizabeth Jenkins.

Federal officials said Ramsay claimed to have destroyed the documents two years ago, but sources close to the investigation said the FBI hoped to recover them Friday, when it served search warrants at the home of Ramsay’s mother and two other sites linked to the former Army sergeant.

Navarro described Ramsay as an enigmatic man who had a high IQ and spoke Japanese, Spanish and German. He once told of trying to rob a bank in Vermont, Navarro said. In recent months, Ramsay had been sleeping in his car near his mother’s home, he added.

Navarro said Ramsay admitted to him in interviews dating back to at least April that he had participated in spying with Conrad, beginning in 1983, when Conrad recruited him. Ramsay said he initially used a 35-millimeter camera to photograph the classified documents, but then switched to more effective videotape.

According to Navarro, Ramsay recorded a total of about 45 hours of videotape.

In an affidavit supporting the criminal complaint against Ramsay in Tampa, the agent said Ramsay told of providing Conrad with classified materials on the use of tactical nuclear weapons by the United States and its NATO allies, military communications and general defense plans for Central Europe.

Navarro said a significant number of the documents carried “top-secret” classification, and many were even more sensitive. According to the FBI agent, Ramsay said he knew the classified documents had been given to agents of the Hungarian and Czechoslovakian intelligence services.

Ramsay, a native of Honolulu, joined the Army in November, 1981, and attended basic training at Ft. Benning, Ga., according to Army records.

After being assigned as a mortar man to the 1st Battalion, 28th Infantry in Ft. Riley, Kan., he was transferred to West Germany in June, 1983, where he worked as a clerk-typist in the archives of the plans unit of the 8th Infantry Division. He left the service as a sergeant in November, 1985.

Staff writer John M. Broder contributed to this story.