Sen. Daniel K. Inouye (D-Hawaii) closed 41 days of Iran-contra hearings by observing that after three months of hearing 250 hours of testimony from 29 witnesses, examining a quarter of a million pages of documents and releasing 1,059 official exhibits, many dealing with some of the most sensitive secrets of the U.S. government, the Iran-contra "story has now been told."

At the same time, Inouye acknowledged, "We may never know, with precision and truth, why it ever happened." More bluntly, despite fascinating hearings that produced extraordinary information, the Iran-contra committees were unable to crack the case. Inouye yesterday described a "chilling" tale of "deceit, duplicity and arrogant disregard of the rule of law"; the tale is also still a mystery.

Ironically, the Democratic and Republican leaders of the two panels who gave closing remarks yesterday all seemed to embrace, with varying enthusiasm, the "fall guy" story, which, according to Lt. Col. Oliver L. North's testimony, was planned in advance: that North and his former boss, Rear Adm. John M. Poindexter, were alone responsible for the worst of the transgressions.

The committtee leaders also absolved President Reagan of direct responsibility for diversion of funds from arms sales to Iran to benefit the Nicaraguan contras. The president has repeatedly denied knowing of the diversion, but he did not testify to the committees. The one admittedly knowledgeable witness who did testify on that question was Poindexter. The public, according to polls, and many members of the committees, according to their public and private statements, found Poindexter an incredible witness, yet this most critical aspect of his testimony was embraced by the committees' leaders yesterday.

How well these committees conducted their inquiry remains to be seen. In the end, the hearings were as untidy and as inconclusive -- if also as essential -- as the democratic process itself. Some of the questioning was sloppy, and many leads were never pursued. By allowing North to dictate the terms of his appearance, the panels opened themselves to second-guessing that will undoubtedly continue for years.

But the committees worked at a considerable disadvantage. Their inability to resolve major conflicts in evidence and sworn testimony was due largely to the fact that so many critical documents bearing on the affair were destroyed, altered or lost.

The man whose testimony was most beneficial to Reagan, Poindexter, was one of the officials who acknowledged destroying key documents. Ultimately, he may prove the most significant of all the witnesses.

Poindexter is a career naval officer with a reputation as a meticulous staff officer trained to follow the chain of command and possessed of a superior intellect and almost "photographic memory," according to his fitness reports. Yesterday the committees released statistics showing that Poindexter set the hearing record for lapse of memory. During his five days on the stand, committee records showed, Poindexter responded 184 times to specific questions by saying, "I can't recall" and "I don't recall."

Poindexter's testimony is vital in another sense. If the story stops with Poindexter, North and the late CIA Director William J. Casey, as the committees seem willing to accept absent conclusive contrary proof, then the judgment can be reached that the Iran-contra affair represented a White House junta, or coup, led by subordinates who seized control of policy apparatus and froze out other U.S. government leaders, including the president. But if this is just the preplanned cover story, then some important people have been engaged in a conspiracy to cover up knowledge of the secret operations. Casey could have been a critical player in such a conspiracy -- by North's account, he was. But Casey died before he had to answer a single question.

But if many critical questions remain unresolved, the Iran-contra investigations produced a wealth of information about the inner workings of the White House during Reagan's second term. Historians will be reaping this harvest for years. Indeed, this material clearly will affect the ultimate judgment on Reagan's presidency. Meanwhile, it provides the public with probably the most intimate and documented look at the inner workings of policymaking at the highest levels of government ever to emerge from a congressional hearing.

And what can be said after the hearings in answer to Inouye's question on "why it ever happened."

The evidence points strongly to Reagan's reaction to one fact -- the taking of U.S. hostages -- and why and how he chose to deal with it in the way he did.

Although the president continues to maintain he was not trading arms for hostages when the first shipments of U.S. weapons went to Iran in 1985, the record disputes him. Release of American hostages seems to have been an obsession in the president's mind during his second term. The committees revealed that the first arms shipments were carried out without a "finding" -- the written presidential authority legally required. The first such finding the president signed on Dec. 5, 1985, specifically approved a straight arms-for-hostages swap and was drafted to cover prior transfers. This is the finding that Poindexter testified he ripped up to save the president "significant political embarrassment" just before Justice Department officials came to the admiral's National Security Council office to review all pertinent arms deal records.

The committees were given an intriguing glimpse into the president's state of mind at that time when Secretary of State George P. Shultz testified about a White House meeting with Reagan and his key advisers two days after the president signed that first -- now nonexistent -- finding. According to Shultz, the president remarked that "the American people will never forgive me" if he did not do everything he could to secure the release of hostages.

This and other testimony strongly suggested that the president was determined to avoid the appearance of impotence in dealing with hostages experienced by his White House predecessor, Jimmy Carter -- and that he still believed the country was as emotionally involved with freeing hostages as it had been in 1980 when he campaigned against Carter on that issue.

In the opinion of many committee members, this preoccupation with hostages dominated White House decision making. Ultimately, policymaking was held hostage by considerations about the hostages. All that followed -- the diversion of profits from deliberately overpriced arms, the allocation of additional secret accounts for "the covert unaccountable network" designed to carry out other extralegal military actions around the world, the "privatization" of foreign policy, the lies, the cover-up attempts -- seem to have stemmed from that original desire to free U.S. hostages by shipping arms to Iran.