One word kept reocurring in Richard Nixon's TV conversation last night, as the former President tried to explain his behavior in the White House. The word was "paranoia."

"Am I paranoic about hating people and trying to do them in?" Nixon asked rhetorically. "And the answer is: at times yes. I get angry at people, but in human terms, as far as I'm concerned, I believe that in individual must never let hatred rule him."

He kept coming back to that subject in his third televised interview with David Frost, explaining his conduct of the war in Vietnam and, as Frost styled it, his war against domestic dissenters at home - the abuses of power that eventually became counts for his impeachment.

"Paranoia for peace," Nixon said at one point, which is as striking as any of the peculiar phrases which entered national usage from the Watergate scandal and Nixon's fall - "stonewall" or "limited hang-out" or the others.

Nixon mentioned the word six times during the interview, without any prompting from Frost. he attributed "paranoia" to his political enemies, he conceded it in himself. It was a moment of rare candor for any politician, especially a disgraced former President, to describe so vividly the fears and resentments that motivated his actions in the White House.

The rest of the program was less compelling, Nixon repeated the defense argument of supreme presidential authority which was examined and rejected in 1974, both by the House impeachment inquiry and the criminal trials of his staff subordinates - namely, that anything a President does is automatically legal.

"When the President does it," Nixon declared, "that means that it is not illegal."

Frost endeavored to penetrate that defensive posture, but Nixon held fast to the formulation. In time of war, Nixon insisted, the President may order illegal acts like burglaries to protect the "national security," to preserve the Republic.

What about murder? If a President could order burglaries, could he order a murder?

"No, no, no," Nixon protested. ". . . I don't know anybody who has been President or is now who would ever have ordered such an action."

Much of last night's program was a somewhat tedious reconstruction of war history - Nixon's version versus David Frost's. The arguments over Vietnam, the invasion of Cambodia, the bombing of civilians, the peace have changed not at all in the intervening years.

Nixon brought up the 22,000 rifles captured in Cambodia and called it one of the most effective operations of the war. Frost accused him of dragging that neutral nation to ruin; Nixon said Frost and his friends in the news media were wrong on that.

This fencing was mostly unproductive. At times, it yielded more preamble from Frost than answer from Nixon. At times, the former President sounded like an old soldier reminiscing, describing once more to the nation how he had refused to take "the easy political path" in Vietnam but held out for an honorable peace.

When Frost turned to the domestic front, the illegal spying and other abuses aimed at political enemies, Nixon's responses revealed - not new facts - but additional insight into his personal resentments toward the Kennedys and Democratic liberals and antiwar protesters.

The opposition, he said, included terrible hypocrites - Democrats who started the war, then turned against it once they were out of power and made it more difficult for him to settle. These people had ill-treated him over the years, it seems.

"Let's take the Kennedy's now," Nixon said. "Did you know that in eight years, after Mrs. Nixon and I had served in Washington for eight years - Vice President, I was Vice President and she as my wife - we were never invited to the White House to a dinner or to a lunch?"

The social slight hurt him. When he returned to the White House as President, he said he made a point of inviting Hubert H. Humphrey, the former Democratic Vice President, to dinner, and also the Kennedy family.

On a deeper level, Nixon said that he and his chief adviser on the war, Henry A. Kissinger, did build up considerable resentment over the leaks of government secrets. Nixon mimicked Kissinger's Germantic accent: "Henry said, I will destroy them."

"We felt this way because the people on the other side were hypocritical." Nixon explained. "They were sanctimontious and they were not serving the best interests of the country. This is why . . . I must say, Henry and I felt so strongly about it. And call it paranoia, but paranoia for peace isn't that bad."

In the review of governmental abuses, Nixon made another concession - using the Internal Revenue Service to punish political enemies is wrong - though he insisted again that it was not illegal.

But the former President made on essential point about the White House misuse of government powers - these practices did not originate with him and presidential abuses should all be judged by a single standard.

"Two wrongs do not make a right," Nixon said. Then he added: "Two wrongs make two wrongs."

The siege mentality of the Nixon White House during those years of domestic turnmoil, he era of mammoth anti-war demonstrations and occasional violence, came through again in Nixon's voice, laden with feeling.

He described Daniel Ellsberg, purveyor of the pentagon Papers, as a "punk." The "best and brightest" of the KennedyJohnson years "proved to be the worst," he said.

"Nobody can know what it means for a President," Nixon explained, "to be sitting in that White House working late at night, as I often did, and to have hundreds of thousands of demonstrators around, charging through the streets.

"No one can know how a President feels when he realizes that his efforts to bring peace, to bring our men home, to bring out POWs home, to stop the killing, to build peace, not just for our time but for time to come, is being jeopardized by individuals who have a different point of view as to how things could be done. Now that's how I felt about it."

Last night's program - like the two previous ones, with two more scheduled - involved edited clippings from 28 hours of interviewing. Frost and his editors last night spliced together questions and answers on two subjects - the war and domestic dissent - in order to show the thematic connections.

Frost himself offered a maudlin closing - suggesting that Richard Nixon was the war's last casualty. [WORD ILLEGIBLE] that melodraamatic sketch.

[WORD ILLEGIBLE] was one of the casualties or maybe the last casualty in Vietnam," he said, "if so, I'm glad I'm the last one."