Through the public testimony of 29 witnesses, the 26 committee members probed details of the Reagan administration's secret arms sales to Iran, the covert network set up by National Security Council aide Lt. Col. Oliver L. North to help the Nicaraguan contras - and attempts by what Inouye called a junta of White House officials to conceal the truth from Congress, Cabinet officials and even the President.
"Certain (National Security Council) staff showed total disrespect for the laws of the United States and our system of government, in effect adopting a position that the end justifies the means," said Senate vice chairman Warren B. Rudman (R., N.H.). "These actions and the attitudes they represent are antithetical to our system of government."
The hearings, said House panel chairman Lee H. Hamilton (D., Ind.), are ''an essential part of the self-cleansing process of our system of government." But self-congratulation was tempered by recognition that important parts of the story may have eluded the committees.
Though investigators interviewed nearly 500 people and reviewed more than a quarter-million pages of documents, there was uneasiness about what was lost in White House shredders, masked behind the conflicting testimony of witnesses and buried with former CIA Director William J. Casey, who died in May, several months after surgery for brain cancer.
"We may never know, with precision and truth, why it ever happened," said Inouye.
At the White House yesterday, aides said President Reagan would address the nation next week on the Iran-contra affair.
"I think the speech will give the President's general views on the hearings and talk about where we go from here and his agenda in the months ahead, but I think it's unlikely that he will go into every detail," said presidential spokesman Marlin Fitzwater.
The focus of attention now shifts to independent counsel Lawrence E. Walsh, whose staff of lawyers and investigators has been secretly gathering evidence of possible criminal conduct. But though a federal grand jury has been empaneled for six months - and Walsh has delivered 25 boxes of sealed evidence to a federal judge - only two minor fund-raisers have been criminally charged.
More indictments are expected. North and former national security adviser Rear Adm. John M. Poindexter have acknowledged that they are targets of Walsh's investigation. However, Walsh must rely on evidence gathered independently of the hearings because both men - and seven other of the panels' witnesses - were promised that their congressional testimony could not be used against them.
Walsh is known to be exploring the possibility of charging North, Poindexter and others with violating a broad criminal statute barring the systematic abuse of power and disregard of public duties. In addition, members of Walsh's staff have been poring over the often-conflicting testimony at the hearings for evidence of perjury. Even witnesses granted partial immunity are not shielded from being accused of lying under oath.
The hearings added many details to the Iran-contra story, but the most important finding, said Rudman, "was the extent to which power was abused by a very small number of individuals."
Essentially, the committees established that:
* Reagan authorized U.S. arms sales to Iran over the objections of both Secretary of State George P. Shultz and Defense Secretary Caspar W. Weinberger. Under Poindexter and North, it quickly degenerated into trading arms for American hostages. Poindexter prevented other ranking administration officials from receiving information on the Iran initiative.
* According to North's testimony, the idea of using Iran arms profits to fund the contras originated with Iranian arms merchant Manucher Ghorbanifar. Poindexter testified that he authorized it without telling Reagan, adding that he was "confident" that the President would have approved it but wanted to save him from political harm in case the diversion became known.
* To carry out their plans, North and Poindexter relied on private operatives - retired Air Force Maj. Gen. Richard V. Secord and Iranian- American businessman Albert Hakim - who took advantage of lack of oversight to profit from the deal; $8 million remains frozen in Swiss and British accounts controlled by the two.
* The NSC circumvented a congressional ban on U.S. aid to the contras in effect between 1984 and 1986. North helped raise funds, plan military operations, provide intelligence to the rebels and - with his superiors' approval - lied to Congress about his role. Reagan knew other countries were contributing money and thanked at least one of them: Saudi Arabia.
* Even after the first details of the arms sales were made public by a Beirut magazine last Nov. 3, North, Secord and Hakim continued to try to negotiate with Iran. They even tried to win release of more hostages by advancing a nine-point plan that, among other things, would have pledged the United States to help overthrow the government of Iraq and pressure Kuwait to release Muslim terrorists held there. Both promises contradicted stated administration policy.
* North, Poindexter and others destroyed documents - including a signed presidential "finding" authorizing a November 1985 arms shipment - to hide politically explosive information from the public, Congress and other administration officials.
"It is also a story of a flawed policy kept alive by a secret White House junta despite repeated warnings and signs of failure, with concession piled upon concession, culminating even in a promise to help secure the release of . . . terrorists who bombed the U.S. Embassy in Kuwait," Inouye said.
But the record the committees have compiled is subject to different
interpretations and continued dispute. "Obviously, there are major differences among the members of the committees over the facts and the significance of those facts," said Rep. Dick Cheney (R., Wyo.), the ranking Republican member of the House panel.
Cheney and Rudman praised Reagan for a degree of cooperation rare in confrontations with Congress. Reagan waived executive privilege and turned over excerpts from his personal diaries to the committees. Republicans also applauded Reagan's changes in NSC staff, procedures and prerogatives.
"To the extent that corrective action was required, the President took it - unilaterally - before our committees had taken a word of public testimony," said Cheney.
But even Cheney joined in condemning the Iran arms deals. "President Reagan has enjoyed many successes during his more than six years in office," said Cheney. "Clearly, this is not one of them."
Cheney also said he saw the Iran-contra affair as "just the latest chapter in an unfinished book about the conduct of U.S. foreign policy." But the other leaders termed it a fundamental breach of trust between the executive and Congress, the sort that democracy cannot tolerate.
"Shortcuts in the democratic process, excessive secrecy in the conduct of government are a sure road to policy failure," said Hamilton. "Policies formed under democratic scrutiny are better than policies formed without it."
The lawmakers spoke after the final witness, Weinberger, said "the interests of the United States were damaged overall" by Reagan's decision to sell arms secretly to Iran. Earlier, Weinberger was asked about an Inquirer Washington Bureau report, published on July 26, which stated that U.S. military personnel supporting sabotage missions had fired on Nicaraguan defenders on two occasions in 1984.
Weinberger dismissed the report as "totally untrue." But in response to questions by Sen. Sam Nunn (D., Ga.), Weinberger said he had not read the article. The story detailed examples of covert military operations directed by the White House and used since the earliest days of the Reagan administration to combat terrorists and perform other covert missions out of view of the Pentagon, CIA and Congress.
The committees are to meet today in closed session to hear testimony from three CIA officials. Declassified transcripts of the proceedings will probably be released later this week. The committees' final reports are not due until October.