Sen. Patrick J. Leahy (D-Vt.), former vice chairman of the Senate Select Committee on Intelligence, resigned from the panel last January after acknowledging he had shown a reporter a draft report on the Iran-contra investigation that the committee had voted not to release to the public.

Responding to reports that Leahy resigned after leaking the document to NBC reporter John Dancy, the committee issued a statement yesterday saying that "the member of the committee responsible for the disclosure" offered his resignation and it was accepted by Committee Chairman David L. Boren (D-Okla.) and Vice Chairman William S. Cohen (R-Maine).

The committee did not identify Leahy as the member in question, but Leahy subsequently issued a statement saying he had "carelessly" allowed a reporter to examine the report to verify his contention that it was withheld because of "major gaps," not as an effort to embarrass President Reagan. He had not intended to disclose details of the report, Leahy said.

"NBC was given the unclassified report without any restrictions on its use by a reliable confidential source," said Robert McFarland, vice president and Washington bureau chief for the network.

Leahy said he learned that contents of the report had been broadcast while he was traveling in the Midwest and immediately went to an airport telephone to call Boren and express concern that "the report was probably a copy which had been sent to {him}."

The cover page of the report, as shown on NBC, contained markings that could be traced to Leahy, according to congressional and other sources. Leahy made no mention of this, however.

Both Leahy and the committee emphasized that contents of the report were not classified as containing sensitive national-security information. The administration has charged Congress with extensive leaking of such information in defending itself against criticism that it has violated legal requirements for informing Congress about covert operations.

The report "had been declassified by the executive branch and therefore the disclosure did not in any way constitute a breach of national security," said Boren and Cohen in the committee's official statement on the incident.

"However, while the draft report was not classified, such a disclosure was not authorized under committee rules without a vote of the committee," they said. "In fact, the committee voted against releasing the report," they added.

In his statement, Leahy said he "allowed the reporter to look at part of the unclassified draft to show that it was being held up because there were major gaps and other problems with it, and not because of a desire to embarrass the president." Some Republicans charged at the time that the report was being suppressed by the Democratic-controlled committee because it tended to distance Reagan from direct involvement in the scandal.

Leahy said he was "angry with himself for carelessly allowing the press person to examine the unclassified draft and to be alone with it. There was no discussion of the disclosure and Sen. Leahy had no intention that any part of the unclassified report be made public."

Leahy served as vice chairman of the committee until Democrats took over control of the Senate this year and he gave up his seniority on the panel to take over as chairman of the Agriculture Committee. Leahy said he told Boren in the telephone conversation he "felt he should continue with his previously announced intention to leave the intelligence committee a few months before the expiration of his term" later this year.

"Sen. Leahy believed this was a suitable way to express his own regret and anger at the release of the unclassified draft," said Leahy's statement, in which he spoke of himself in the third-person.

Leahy's resignation was formally tendered and accepted Jan. 13, according to the committee.