A presidential oversight board's 1985 investigation of charges that the National Security Council staff was violating a congressional ban on aid to the contras was limited to a 30-minute talk with one official, a five-minute chat with Lt. Col. Oliver L. North and a quick document review, the board's lawyer testified yesterday.

Bretton G. Sciaroni, general counsel of the Intelligence Oversight Board (IOB) since mid-1984, told the Iran-contra committees that North and NSC staff attorney Cmdr. Paul B. Thompson both assured him that the allegations were untrue.

The 35-year-old Sciaroni, who failed bar exams four times before passing one in Pennsylvania, where he has never lived or practiced, said he was not shown key files that documented North's role in raising funds and buying weapons for the Nicaraguan rebels. But he added that he still would not change his Sept. 12, 1985, legal opinion that the NSC staff was not covered by the ban.

Some members of the congressional investigating committees challenged the adequacy of Sciaroni's investigation, suggesting that the IOB needed a bigger staff and subpoena power. Sciaroni retorted: "Well, my investigation was probably as thorough as the one that had been conducted by the Hill."

Previous testimony has shown that Congress was misled about North's activities by North and his superiors, national security advisers Robert C. McFarlane and John M. Poindexter.

Sciaroni, the first witness called by committee Republicans, spent much of his four hours of testimony listening to members alternately defend and attack his conclusion that the Boland Amendment did not apply to the NSC staff.

The IOB is a little-known entity, created by President Gerald R. Ford in 1976 after disclosures of illegal conduct by U.S. intelligence agencies. Its three unpaid members and one lawyer are supposed to serve as a sort of super inspector general, checking complaints about the legality of spy agency activities.

The Tower review board report on the Iran-contra affair noted that the IOB was "an odd source" of legal advice for the NSC, because its role is to review the legality of other agencies' actions rather than originate opinions.

Sciaroni said he started his legal research and the inquiry into North's activities after reading press allegations against the NSC aide in August 1985. He denied a suggestion by Sen. Paul S. Sarbanes (D-Md.) that several opinions he wrote for the NSC served as a legal "cover" so its staff could aid the Nicaraguan rebels.

But he said he too wondered why lawyers from the NSC, the White House staff or the Justice Department were not asked to address the issue. "I don't know why my opinion was the only opinion," he said.

Rep. Edward P. Boland (D-Mass.), author of the ban, said he found Sciaroni's testimony "an enlightened description" of the administration's only analysis of the legal issues surrounding its controversial covert aid to the contras. "Think about that and consider what it tells us about the value the White House placed on adhering to the laws," he said.

Sciaroni acknowledged, under questioning, that he had failed the California and District of Columbia bar exams twice each before being hired for the $62,000-a-year IOB post, his first job as an attorney. He finally met the legal qualification, he said, by passing the Pennsylvania bar exam so he could be "waived in" to practice in Washington.

In April 1985, Sciaroni sent North a draft legal opinion on "the legal basis for covert action" in Central America. He attached a note asking North to "give me your comments (at your leisure of course). Thanks."

Sciaroni said, in reply to a question from Sarbanes, that he often sent drafts of his opinions to officials from government agencies and assumed that North "knew something about covert action." Two of Sciaroni's predecessors as general counsel of the IOB said yesterday that such legal work for the White House was rare in their tenure.

Traditionally, intelligence sources have said, the board investigated such questions of propriety as the payment of millions of dollars to King Hussein of Jordan, or, under Sciaroni, the allegation that the Central Intelligence Agency had approved the publication of an assassination manual for the contras.