In three days of congressional testimony, former national security adviser John M. Poindexter has illuminated three underlying attitudes that strongly contributed to the Reagan administration's Iran-contra disasters -- a White House preoccupation with secrecy, a distrust of the press and a desire to circumvent congressional oversight of secret operations.

Rear Adm. Poindexter summed up those attitudes in one revealing remark yesterday to the Iran-contra committees: "I simply didn't want any outside interference."

By "outside interference," Poindexter meant Congress. His comment came while he was offering a broader rationale for withholding information from Congress about the National Security Council's role in assisting the Nicaraguan contra forces. His reasons were twofold:

"One," he said, "we wanted to return to a covert implementation of the policy. If it had . . . become public as to exactly what we were doing, there would have been all sorts of press inquiries down in Central America. It would have been a very hot political issue. It would have caused problems for our friends and supporters in Central America. And if we had revealed all those details -- because the press understood it was a controversial political issue in the Congress -- there would have been a lot of attention to it, which would have essentially destroyed our ability to carry on the support for the contras under those very difficult situations."

His second concern was that exposure of the secret operations might lead to more restrictive congressional legislation "in some new form of the Boland Amendment," banning direct U.S. military aid to the contras. That's why he didn't want "any outside interference."

These attitudes contributed to the atmosphere of secrecy that has permeated the White House in the Reagan years. Poindexter's testimony has been revealing, in part because it helps answer one of the investigating committees' major questions -- what Senate chief counsel Arthur L. Liman told the admiral is the desire to understand "what was going through the mind of people like you who made the decisions."

According to Poindexter's testimony, there was a strong concern about maintaining secrecy to stop press leaks and forestall congressional inquiries. Poindexter said he did this without any apparent regrets and, it would seem, without an appreciation that, in the end, those attitudes proved destructive for the policy purposes he sought to achieve.

Frustration over leaks is hardly unusual among government officials in Washington. But Poindexter's remarks disclosed a deeper emotion. That was true of his bitterly expressed feelings toward the press in general, but The Washington Post in particular. He made several critical remarks about The Post, and at one point said he did not regard it as an "accurate source."

Poindexter's testimony was replete with evidence of his intent to withhold information from the Congress and the public, and even from other high administration officials. Such testimony brought a memorable -- and, again, revealing -- exchange between Senate select committee Chairman Daniel K. Inouye (D-Hawaii) and the president's former national security adviser.

Inouye said: "When we sit here and listen to your testimony, in which you tell us that you have either withheld information from or misled or misinformed the Congress of the United States, that you have withheld information from the president, that you have either withheld information from or misled or misinformed the highest-ranking Cabinet members of the United States, that you have withheld information from your most trusted deputy, {Lt.} Col. {Oliver L.} North -- I don't think it is improper for any member of this panel to characterize that testimony as being incredible, mind-boggling, chilling."

Poindexter immediately responded: "Chairman Inouye, I don't think it is fair to say that I misinformed Congress or other Cabinet officers. I haven't testified to that. I've testified that I withheld information from Congress. And with regard to the Cabinet officers, I didn't withhold anything from them that they didn't want withheld from them."

It was apparent that the committees did not accept Poindexter's rationale. "Government must operate in good faith," Senate committee Vice Chairman Warren B. Rudman (R -- N.H.) told him yesterday afternoon. "It is the trust that we put in each other in government that makes it work."

He received a similar lecture from Rep. Henry J. Hyde (R -- Ill.), one of the strongest supporters of Reagan and contra aid on the committees: "The problem with deceiving Congress is that your friends get deceived and they go out and talk to the media and do television programs and insist that what you have told us is true, and it can be very embarrassing. And it affects our credibility."

The person who has suffered the greatest damage to his credibility in the Iran-contra affair has been President Reagan. Poindexter's stated decision to withhold knowledge of the contra diversion from the president because he wanted to give Reagan "plausible deniability" was the subject of the most intense questioning yesterday, as, undoubtedly, it will be for a long time to come.

House counsel John W. Nields Jr. asked a series of questions about the state of mind -- both Reagan's and Poindexter's -- that produced such a decision.

It went like this:

Nields: "And my question to you is this, based on your 5 1/2 years of experience with him, what led you to believe that he would want deniablity, as opposed to responsibility, for an embarrassing political decision?"

Poindexter: "That was a personal judgment on my part."

Nields: "Did you believe it is what he would want?"

Poindexter: "The situation -- I think -- was very clear in my mind. As I have testified, I felt confident that he would want to do this. He was very secure in his belief that it was the only way that we could bring about a democratic change to the government in Nicaragua . . . . "

What Poindexter meant was: the "only way" was the secret way.