A CIA taping system for overseas communications recorded several conversations that are "pertinent" to the Iran-contra affair, including one between then-CIA director William J. Casey and then-national security adviser John M. Poindexter after the Iran arms sales became public last November, according to information released yesterday at the Iran-contra hearings.

Poindexter testified that he called Casey, who was traveling in Central America, and asked him to return to Washington so he could help explain to Congress the administration's secret Iran arms sales. He said he did not realize the call was taped.

The Iran-contra congressional committees have received a transcript of that call. Members said it would be released when it is declassified. The CIA is reviewing all other tapes involving Casey, a senior administration official said yesterday, and any additional "relevant" transcripts have been, or soon will be, turned over to congressional committees and independent counsel Lawrence E. Walsh.

The official declined to say if the tapes contain any significant new information, and there was no indication yesterday that committee members expected any startling disclosure in the tapes. The White House declined to comment.

Walsh and congressional investigators are attempting to determine if Reagan administration officials, including Casey and Poindexter, participated in a cover-up of the arms sales to Iran. At the time of the taped conversation -- the week of last Nov. 17, according to testimony -- the diversion of arms sales profits to the contras was still a closely guarded secret.

According to testimony before the congressional committees, only three people in the U.S. government knew of the diversion -- Poindexter, Casey and fired National Security Council staffer Lt. Col. Oliver L. North.

Senate counsel Arthur L. Liman said yesterday, "The CIA has a special voice communications system which is used in lieu of cable traffic for overseas communication of an operational nature on occasion . . . . During the course of our investigation, we have requested and received transcripts of pertinent communications." He said the CIA has an index of all calls.

The existence of the Poindexter-Casey tape became public yesterday when Poindexter was questioned about the false chronologies put together under his direction by the White House after the disclosure of the Iran arms deals.

Poindexter said that he did not know he was taped and had not read the transcript of the call but that he had "a vague recollection of the conversation." He said his actions last November were not intended as a cover-up but rather to "protect as much of the information about the project as possible . . . to get some of the hostages out, and we wanted to salvage what we could, of the second channel" of secret contacts in Iran.

Richard W. Beckler, Poindexter's attorney, said he became aware of the transcript last week and indicated that he had seen it. "I view it as a critical document, as a contemporaneous statement of what Admiral Poindexter's intentions were at the time that he asked Bill Casey to come back up . . . I would request again that all expeditious means be used to declassify that," Beckler said.

During his six years as CIA chief, Casey traveled extensively overseas and was a habitual user of the telephone. He did not like the secure voice systems, which are often unreliable and provide inferior voice quality to an "open," or regular, telephone line. Conversations on open phone lines were not routinely taped.

It was 14 years ago to the day -- July 16, 1973 -- that Alexander P. Butterfield first disclosed the existence of President Nixon's secret taping system in the White House, but there was no indication yesterday that the CIA's tapes will provide the kind of wealth of information that the Nixon tapes did.

In testimony last week, North said he spoke with Casey about twice a week, often on the telephone. North was not asked in his public testimony whether he ever spoke with Casey through the CIA's secure voice system when either of them was abroad.

Casey died in May, and since then investigators have reviewed his records in an effort to determine if there are any documents, notes or transcripts that reveal his role in the Iran-contra affair. "There are no notes of meetings, and we have not found, at the CIA, a stash of Casey documents that tells much," one source said recently.