Federal prosecutors have offered former CIA agent Edwin P. Wilson, held in federal custody on charges of shipping explosives and providing terrorist training for Libyan ruler Muammar Qaddafi, a maximum 15-year prison term if Wilson pleads guilty and agrees to cooperate with the government.

Wilson, 54, has not accepted that offer, which apparently was made shortly after his capture in June in New York, according to a knowledgeable source.

The details of the offer were unclear, but one source said he understood it involved Wilson's agreeing to plead to several separate felony counts that would total a maximum of 15 years in prison. A 15-year sentence, under federal guidelines, would mean that Wilson, who faces more than 50 years in prison if convicted of all charges against him, would be eligible for parole after about nine years.

If Wilson cooperated to the satisfaction of prosecutors, however, some or all those felony sentences could run concurrently, which would mean Wilson could be released possibly after as little as three years in prison.

Wilson's attorneys have said he was working with the CIA while he was in Libya, a claim the CIA has repeatedly denied.

Prosecutors declined last night to confirm or deny that the plea offer had been made. But one source said it was reasonable to assume that negotiations on a plea began virtually from the moment Wilson was indicted here in April 1980 on charges of shipping explosives and timing devices to Libya, providing training for terrorists for the Libyan government and conspiracy to assassinate an exiled opponent of Qaddafi.