THE INNER LOGIC of Richard Nixon's whole presidency was illuminated with stark clarity in his interview with David Frost last night. He "had a responsibility which was, above everything else ," to end the Vietnam war in his chosen manner, he said. To keep Hanoi from taking heart from the anti-war protesters and refusing to negotiate, he felt compelled to put down "dissent coupled with violence, and, ah, advocacy of violence." So he commissioned the illegalities and improprieties known collectively as Watergate. As he reflected last night, "when the President does it, that means that it is not illegal. . . The people on the other side were hypocritical . . . sanctimonious . . . not serving the best interests of the country." Paranoia? "Paranoia for peace." And, he concluded, it worked: Le Duc Tho bowed and the war - by which Mr. Nixon means the American combat role - "finished . . . on an honorable basis," and there ensued "a peace" that lasted, by his measuring, for some two years.

Well, there it is - the real Nixon Doctrine, a genuinely historic theory of governance that was implicit in his earlier defense of wrongdoing but had not been stated so explicitly before. Once Mr. Nixon accepted the premise that his war policy counted "above everything else," it followed all too grimly that he would elaborate a doctrine of gross presidential privilege - "when the President does it, that means that it is not illegal" - to neutralize such perceived obstacles as the citizenry's legal and peaceable dissent. That is the logic of the national security state. The flaw, of course, lies not in the reasoning but in the premise. In the judgment of many Americans at the time, and in the judgment of many more now, it was simply not as important as the former President insists to end the war in his way. He had choices other than "bugging out." We will not rehearse the argument. We merely note that, whatever the theoretical rationale for a President to rise above the law in an authentic national emergency, this was not such an emergency.

Like Lot's wife, whose refusal to look back Mr. Nixon hailed last week as a personal model, he is not in a self-critical frame of mind. The image of himself as "the last American casualty of the Vietnam war" is too comforting. To look back would undercut his thesis that, while he blew the "pipsqueak Watergate thing," he "did the big things rather well." Actually, he did the Watergate thing rather well. But for the chance disclosure of the tapes, he might have come away clean. But Vietnam was a big thing, perhaps his biggest. And the awful irony of it all is that the misdeeds and abuses he engaged in to salvage the big thing - his flawed and failing policy in Vietnam - lead inexorably to that "pipsqueak thing" called Watergate that undid him in the end.