CHARLOTTE, N.C. (AP) _ A Marine accused of trying to sell nuclear, biological and chemical warfare information to Soviet and East European spies was convicted at a court martial last year and is serving a prison term, the FBI announced Tuesday.

Robert E. Cordrey, 23, a private, was convicted Aug. 13 of 18 counts of failing to report contacts with citizens of communist nations, and was sentenced to 12 years at hard labor, said FBI agent Robert Pence.

The case was not disclosed before Tuesday because it was part of an ''extremely sensitive investigation,'' said Pence.

Cordrey, of Millsboro, Del., taught at a Camp Lejuene school that tells Marines how to survive when nuclear, biological or chemical weapons have been used, said Capt. Craig Fisher, a Camp Lejuene spokesman.

Authorities began an investigation after learning April 12 that Cordrey was trying to sell material related to his school to Soviet, Czechoslovakian, East German and Polish agents, Pence said.Fisher said Cordrey telephoned the agents and offered to sell the information.

Cordrey was arrested May 16 and immediatedly placed in pretrial confinement pending his court martial, Pence said.

The court martial was not closed, although no attempt was made to publicize the case, said Naval Investigative Service agent G.W. Aldridge.

''He entered a guilty plea and didn't contest it, so there was nothing classified that was disclosed'' during the trial, Aldridge said.

Cordrey, whose sentence included forfeiture of pay and a dishonorable discharge, is tentatively scheduled to be released from the brig at Camp Lejeune in December under a pretrial agreement, Fisher said.

''Hard labor'' involves any type of work in prison, such as cutting grass or making boxes, Fisher said.

All Marines under the rank of master sergeant take the courses at the Nuclear, Biological and Chemical Defense School, known as the NBC School.

''They're not designed to teach how to use the weapons ... (but how) to take steps if you are in that type of environment,'' said Fisher.''If he was an instructor, that's what he'd be involved with - equipment, procedures and how to operate them.''

Pence, Fisher and Aldridge declined to say what type of material Cordrey tried to sell, how much money was involved or how he was caught.

''I know this raises a lot of questions, but this is an extremely sensitive investigation,'' Pence said. ''I can't give any more information than that at all. Approval to say that much came from headquarters yesterday.''

He said the FBI decided to publicize Cordrey's case only now because there is no longer any pending investigation related to it.

''We haven't been able to talk due to the sensitivities that now have been resolved,'' he said.

North Carolina's military bases remain a major target for foreign spies, along with the state's growing microelectronics business and its two ports, Pence said.

''They (the bases) still are a big problem,'' he said. ''We are constantly being vigilant and working with the military services. This is an example of that vigilance.''