WASHINGTON -- The Iran-contra prosecutor has acquired tapes of hundreds of telephone conversations between Central Intelligence Agency headquarters and CIA agents in Central America, providing a lode of data on Oliver L. North's secret arms pipeline to Nicaraguan rebels, government officials and others involved in the inquiry said yesterday.
The conversations included corroborating evidence that helped the prosecutor, Lawrence E. Walsh, secure a plea bargain this week from a CIA official, Alan D. Fiers Jr., who has implicated his superiors in the arms scandal.
One official said that the telephone conversations were retained by a recording system that was ordered installed in the CIA's seventh-floor operations center in Langley, Va., in the early-to-mid-1980s. Others said that the system, whose existence was not previously disclosed, was ordered in 1984 by Clair E. George, who then commanded the agency's worldwide network of agents under then-CIA Director William J. Casey.
They said that Mr. George had the recorders installed and that he assigned stenographers to transcribe all conversations on secure lines to overseas posts, so that a written record would exist of instructions by senior agency officials to subordinates in the field.
Mr. George has become a focus of the inquiry as a result of the plea bargain negotiated with Mr. Fiers, who is now cooperating with the investigation. According to court documents, Mr. Fiers has alleged that Mr. George ordered him in 1986 to conceal his knowledge of Mr. North's clandestine arms network from Congress.
The recording system became operational in 1984, about the time Mr. Fiers was named chief of the Central America Task Force, a CIA division that supervised the agency's relations with the Nicaraguan rebels.
Most communications between CIA headquarters and agency officers overseas are conducted by coded cable, but Mr. Fiers and his superiors used the monitored telephones regularly for conversations with station chiefs in Honduras, Costa Rica and elsewhere, officials said.
A CIA spokesman, Mark Mansfield, said last night that the agency would not comment on any aspect of the Iran-contra inquiry, including whether any tapes had been turned over to Mr. Walsh's office.
Mr. Walsh's team of prosecutors originally acquired the tapes during their investigation of Joseph F. Fernandez, a former CIA station chief in Costa Rica. He was indicted in 1988, but the Fernandez prosecution was quashed by the Justice Department grounds that it would disclose valuable state secrets.
The significance of the taped conversations in the case of Mr. Fiers apparently did not surface until this year.
One official said that even in transcribed form, many of the taped conversations were extremely difficult to understand and to relate to the events occurring in Nicaragua and in Washington at the time. They nevertheless "certainly were at least the substantiation for the allegations made by others" that eventually led investigators to Mr. Fiers, the official said.
Some witnesses in the inquiry have expressed surprise at the intimate knowledge of CIA workings displayed by investigators during their grand jury questioning -- knowledge that came, at least in part, from the transcribed conversations.
As described by officials, the CIA's decision to record the telephone calls sprang from the same impulse for a permanent record of conversations that figured in the famous Oval Office tapings in the Watergate scandal.
Agency officials were described as feeling that there was a possibility of orders' being misunderstood if no records were kept of phone conversations between CIA headquarters and CIA stations around the world.
"While people have secure telephones at their desks for conversations around town and within headquarters, and they could theoretically use those phones to make calls overseas, the operations directorate required them to use the system whereby they could only make calls from a controlled room," one former administration official said.
"They'd make a call, and someone would be listening and tape-recording it in a chair next to them and making notes."
It could not be learned whether Mr. George or his superior, Mr. Casey used the system for their own calls, but several intelligence officials and former intelligence experts said last night that that was unlikely.
Those officials, as well as others who provided information about the taping system, spoke on condition of anonymity.