The House and Senate Iran-contra committees announced yesterday that they have reached an agreement with a lawyer for former White House aide Oliver L. North that will allow North to begin testifying publicly on July 7.

The agreement was disclosed near the conclusion of a day of hearings at which the activities of the former National Security Council official in the Iran-contra affair were once again a focus of attention.

The committees revealed that Marine Lt. Col. North was the author of a Dec. 9, 1985, memo outlining what became the core of the arms-for-hostages plan adopted by President Reagan on Jan. 17, 1986. North suggested the option of direct deliveries of U.S. weapons to Iran -- instead of shipments from Israel, the original plan -- and proposed using retired Air Force major general Richard V. Secord as the "conduit" in the transactions. This was the scheme adopted.

The possibility that North might face criminal contempt proceedings rather than testify under the committees' grant of limited immunity receded yesterday when Sen. Daniel K. Inouye (D-Hawaii), chairman of the Senate select committee, announced that a one-week impasse with North's lawyers had ended.

Committee members, sensitive to charges that they had made concessions to North, stressed that they have given him no binding "commitments." Instead, they said, they had outlined their "intentions" in a letter worked out with one of North's attorneys, Brendan V. Sullivan Jr., and sent to Sullivan yesterday.

Describing himself as "very pleased," House committee Chairman Lee H. Hamilton (D-Ind.) said: "In this agreement we did not make any concessions; we set the terms and the timing {of North's appearance before the committees}."

Nevertheless, as described by committee sources, the understanding meets most of the concerns originally expressed by North's lawyer and will sharply curtail investigators' opportunities to ask North preliminary questions in closed session before his public appearances.

The understanding calls for North to turn over documents and appear initially on July 1 in closed session -- but not under oath -- to discuss Reagan's knowledge of the diversion of profits from the sale of U.S. arms to Iran to support the Nicaraguan contras. He will then be sworn in and asked a few key questions based on the interview.

Relevant documents from North's NSC files, currently in the possession of the committees, will be made available to him, the sources said.

Inouye said the arrangement for the limited preliminary questioning had been deemed sufficient by the House and Senate counsels, who worked out the understanding with Sullivan. In the letter, the committees say they anticipate that his public testimony will last no more than a week and that they do not expect to call him back after that.

Not all members of the panels were happy with the arrangement. Rep. Jack Brooks (D-Tex.) called the deal with North "a rotten precedent for Congress."

As has frequently been the case in the seven weeks of public hearings, North emerged yesterday as the central -- but absent -- figure.

Yesterday's sole witness was former CIA general counsel Stanley Sporkin, who provided the most detailed inside look to date at the process that led to the official presidential intelligence "finding" that authorized U.S. arms sales to Iran in January 1986.

Sporkin, a self-styled protege of the late CIA director William J. Casey, who brought him to the CIA as general counsel then helped him win a federal judgeship last year, disclosed that:He does not know "to this day" whether Reagan ever signed an intelligence finding he drafted on Nov. 25, 1985, "ratifying" a possibly illegal event that had already taken place: the use of the Central Intelligence Agency to help Israel deliver American-made missiles to Iran. During preparations of a later legal document to authorize a subsequent initiative with Iran, North argued unsuccessfully for deleting any reference to securing the release of U.S. hostages, apparently because the reference would tip off the State Department about the initiative's real purpose. North indicated that he would be "just as happy" not to have the CIA involved in the Iran initative. And John A. McMahon, then the CIA's deputy director, was also not anxious to have the agency involved "unless we were running the whole operation."

He had called national security adviser John M. Poindexter in January 1986 to inform him that Secord, the principal private operative in the Iran initiative, had been denied a CIA security clearance in 1983 because of an investigation of his ties to Edwin P. Wilson, the former CIA official convicted for arms trafficking with Libya.

Poindexter said he would look into the matter. Several days later, Secord attended a meeting with Sporkin in the White House Situation Room at which details of a forthcoming new initiative with Iran were discussed. Sporkin said Secord's presence at that session made him uncomfortable.

Sporkin, told the committees that he became aware of an Iran initiative on Nov. 25, 1985, when McMahon called him about an "extremely sensitive matter."

The matter, which had been described previously in testimony, involved help that the CIA had provided to the Israeli delivery of Hawk antiaircraft missiles to Iran on the night of Nov. 23. It was the second sale of Israeli-owned U.S. weapons that had been approved by the U.S. government. The first occurred the previous August but involved no direct American assistance.

Following McMahon's call, Sporkin said, he met for 20 minutes with two CIA operations officers and determined that the CIA's role would require a presidential "ratification," a word he said was preferable to "retroactive approval."

His initial draft of the authorization, called a finding, was completed the next day. It said the sole purpose of the covert sale of munitions to the government of Iran was to help secure the release of the American hostages. It provided after-the-fact presidential approval for the just-completed transaction and for subsequent deals, and it directed then-CIA Director William J. Casey "not to inform Congress" until the president directed otherwise.

In later testimony, Sporkin said the intent was to notify Congress once all hostages were released and, in any case, before the end of the Reagan presidency. By statute, the CIA is required to notify Congress of covert activities before they occur in most cases and in a "timely" fashion if they are so urgent that prior notification is impossible.

Sporkin acknowledged that the recommendation to withhold notification of Congress was one of only two instances during his service as the CIA's top lawyer in which he suggested this course. He did not identify the second instance.

The finding attempting to cover the November 1985 Hawk sale retroactively has never been located. Sporkin said a copy with the president's signature was never returned to his office files -- a departure from usual practice.

The potentially embarrassing issue for the administration was the possibility that it broke the law prohibiting recipients of U.S. weapons from reshipping them to third countries -- in this case, Israel shipping arms to Iran. Sporkin's office was aware of this problem and reminded him in a Jan. 7, 1986, memo that the U.S. Arms Export Control Act required notification of Congress in such circumstances and that the receiving government had to certify the weapons would be used only in self-defense -- a restriction that the Iranian government would never accept.

In a comment that elicited additional questions from committee members, Sporkin declared that "you can override specific statutes with a covert finding." In subsequent exchanges with Sporkin, three senators, William S. Cohen (R-Maine), Sam Nunn (D-Ga.) and George J. Mitchell (D-Maine), indicated that they were troubled by that view, which appeared to give wider latitude to the president in covert actions than intended by Congress.

As the battle continued in the administration over the possibility of a broader Iran initiative in late 1985 and early 1986, legal concerns about transferring weapons through Israel apparently weighed in favor of direct involvement by the U.S. government.

Documents released yesterday portray North as an ardent supporter of a stepped-up initiative with representatives of Tehran.

North, in the Dec. 9, 1985, memo, describes the results of a recent meeting in London involving North, national security adviser Robert C. McFarlane, Secord and Iranian intermediary Manucher Ghorbanifar as "inconclusive." Previous testimony by Secord had described the meeting as a disaster. And Secord quoted McFarlane as afterward calling Ghorbanifar "the most despicable person he had ever met."

By using Secord as an intermediary, North proposed in one "option," it would be possible to "control Ghorbanifar."

It was around Dec. 10 that Secretary of State George P. Shultz and Secretary of Defense Caspar W. Weinberger believed the initiative was dead, they have said. But on Jan. 2, 1986, Sporkin testified, North called and dictated an expanded proposed presidential authorization.

Three days later, Sporkin and North met Casey at Casey's home. North presented the CIA director with a copy of the new finding and a cover letter. The cover memo, from Poindexter to the president, reported that the Israelis were prepared to begin selling military materiel "unilaterally" to "western-oriented Iranian factions," to achieve a "more moderate Iranian government."

The memo stated: "The Israelis and the Iranians with whom they are in contact agree that the continued holding of the five American hostages in Beirut will be immediately solved through commencement of this action."

However, Sporkin said, he noticed there was no mention of hostages in the legal document, or finding, that was to have gone to the president for his signature.

Confronting North in the corridor, Sporkin asked, "Tell me again . . . why we're not putting hostages in this document." North, he said, mentioned that "either the secretary of state or the Department of State did not want it in."

Sporkin recalled saying that it did not "seem right" to leave out the main purpose of the initiative. The two men put their cases before Casey, who sided with Sporkin. The final document, signed by the president Jan. 17, mentioned hostages.

Senate counsel Timothy C. Woodcock asked Sporkin: "In other words, you're not going to have a situation in which you had a covert finding that was so covert that there were terms that were even secret from the terms of the finding itself?"

Sporkin replied, "I'll leave what I said."