A Fairfax County judge, advised by a prosecutor that most of the 12 Libyans involved in the takeover of their country's student aid office in McLean last month have "very shadowy" backgrounds, yesterday refused to reduce their bonds.

"We have had great difficulty in verifying anything with these 'students,' " Commonwealth's Attorney Robert F. Horan told General District Judge Conrad Waters. "The background of these individuals is very shadowy, very, very nebulous."

Waters then rejected a defense attorney's request to lower the bonds of $15,000 and $30,000 under which the men had been held.

Most had told police after their arrests Dec. 22 on charges of abducting workers at the student center that they were attending American universities. But Horan said yesterday that, except for one man freed on bail late Tuesday, "not a single college has yet verified that these people are students."

Horan added that one of the men has been convicted of forgery in Milwaukee and another is wanted by police in Gainesville, Fla., on a 1980 charge of aggravated battery.

Many of the Libyans also have been unable to produce their passports, according to both the prosecutor and defense attorney Sebastian K.D. Graber. Graber, who said that his clients are anxious to prove their innocence in court, said that the passports of some of them are in Libya.

Verne Jervis, a spokesman for the Immigration and Naturalization Service, said separately that the agency has interviewed the Libyans and also has questions about them.

"We have not fully established their identity and immigration status to our satisfaction," he said.

The Libyans are charged with abducting three employes of the People's Committee for Students of Libyan Arab Jamahiriya Inc., a private corporation that provides scholarships to Libyan students.

The nine-hour takeover ended peacefully and with no injuries, but with a reputed $250,000 damage to the building.

The protesters claim the center is used by Libyan leader Col. Muammar Qaddafi to spy on Libyan students, a claim that the organization denies. Horan said that a Libyan specialist with the FBI had studied documents the protesters seized during the takeover, and the documents had failed to back up their spy claims.

Later, Horan said that Graber had asked him to consider reducing the abduction charge to trespassing and destroying private property for those defendants with no previous arrest records. Horan said he would consider the request.

The Libyan who has been released on bail is Jamal M. Buzayan, a research fellow at the University of California at Davis, who had been granted political asylum in the United States before the McLean incident, according to Horan and Jervis.

Horan yesterday identified Buzayan as "John Doe 11," who acted as spokesman for the group last week and asked the court to withhold their names because they feared reprisals. The court denied the request.