For the Iran-contra hearings, still a living organism, though clearly with the life ebbing away, post-mortems are already being conducted.

Here are some. From the we'll- never-know school, strengthened by the confounding, contradictory and forgetful testimony of Rear Adm. John M. Poindexter, Senate select committee Chairman Daniel K. Inouye (D-Hawaii):

"I am now reaching the conclusion that, much as we try, we may very well end up our investigation not really knowing what actually happened," Inouye told ABC television after the hearings resumed this week, "because here we have an admiral and the colonel {Lt. Col. Oliver L. North} not agreeing on certain basic facts. The colonel says he sent certain memos on diversion to the admiral. The admiral says that he's never heard of that, he doesn't recall receiving anything like that. Now, these are basic things."

From the they-were-all-a-waste- of-time-and-money school, the president's unregenerate defender, Sen. Orrin G. Hatch (R-Utah):

"As we near the end of these hearings . . . I'm struck more and more how terribly overblown this whole affair has been. We have elevated the art of beating a dead horse to new heights."

From the grave-constitutional- breakdown school, the salty Iran-contra critic, Rep. Jack Brooks (D-Tex.):

"You wanted to exclude all the elected officials from knowledge of some of the most important and far-reaching areas of foreign policy," Brooks sternly lectured Poindexter. "Now . . . is this not precisely the kind of thing that our Founding Fathers were trying to prevent when the Constitution placed the authority and the accountability for these decisions in both the Congress and the president?"

These comments may foreshadow diverse opinions of committee members in their final report this fall, but it is too early for any final judgments yet on the Iran-contra hearings, especially since the most critical questions remain largely unexplored.

For nearly 10 weeks, the hearings have documented an amazing level of deceit within the highest levels of the administration. These revelations already have had significant impact on domestic and foreign policies, the relationship between Congress and the White House, the president's credibility and Americans' ability to trust their leaders.

The hearings have produced a wealth of damning information about the ways in which secrecy and ideology dominated presidential decision-making in the second Reagan term. This record has diminished Reagan's stature and jeopardized his ability to conduct his office in the closing months of his presidency. It also seems certain to affect negatively his standing in history.

With Poindexter's testimony, the question about the president's knowledge of the diversion of Iran arms sale profits to Nicaraguan contra forces has been, if not put to rest, at least put aside. It seems almost certain now that there will be no impeachment. As Inouye says, given the number of contradictions, the truth about that aspect of the affair may never be known.

We thus know much about what happened but not nearly enough about why and how. Here, the forthcoming testimony of key Cabinet officers and presidential advisers, including former chief of staff Donald T. Regan, Secretary of State George P. Shultz, Defense Secretary Caspar W. Weinberger and Attorney General Edwin Meese III, is crucial. Of all the unanswered questions still before the committees, none looms larger than this: Why didn't anyone around the president -- and the president himself -- ever ask a single question about what had happened after they say they first learned about the diversion?

That's what Sen. George J. Mitchell (D-Maine) was getting at when he asked Poindexter why, in the week immediately preceding his resignation, "not one of them ever asked you to explain your decision or whether you had told the president." The admiral's response cries out for answers:

"There were three significant meetings involved . . . . There was a short meeting with Ed Meese in my office on Monday, Nov. 24. There was a meeting -- well, there were four, I guess. The second meeting was with Ed Meese in his office the morning of the 25th. Don Regan came into my office while I was eating breakfast. It was about a five-minute conversation. And then I had about five or 10 minutes with the president and the vice president, Don Regan, Ed Meese at 9:30 on that morning. All of these conversations were very general in nature, not any sort of inquiry or investigation or detailed questions, and I was not asked those questions."

Why not?