"I can't explain myself, I am afraid, sir," said Alice to the Caterpillar, "because I am not myself, you see." The Caterpillar didn't get it, but never mind. Alice's predicament in her Wonderland is not so different from Ronald Reagan's in his: the White House, Washington, the world at large. He cannot explain how he proposes to deal with arms control or budget deficits in the way that even some of his strongest supporters are now recommending, because to do so, he would not be himself.

The remedial measures that are being widely recommended by Republicans as well as Democrats (including voices within the administration) simply do not fit those Reagan beliefs that have hardened over a lifetime into fixed principles and been raised to the level of what he calls a "philosophy."

And that strikes me as an element too little emphasized in the outpouring of midterm report cards on the president's performance. True, some of the cannonading of criticism has zeroed in on the president. But by and large it is the Reagan administration that is being called to account.

The keen noses of The New York Times and The Wall Street Journal have sniffed, respectively, "the stench of failure" and a "whiff of panic" at the White House. There has been talk of "administration" drift and disarray. Deep doubts have been raised as to whether the "administration" can pull itself together before its work gives way to the paralyzing distractions of next year's presidential campaign.

The answer suggested by some critics is that, yes, a lot of the trouble can be solved by a stronger presidential lead and deeper personal involvement; by compromising on defense spending; by reshuffling the arms-control hierarchy and a somewhat more forthcoming U.S. approach to the several arms- control negotiations under way.

But it is in precisely the area of how to deal with the Soviet Union that Ronald Reagan would collide with himself in any serious effort to alter course. Here we are not talking about tactics or dogma--as in supply-side economics. We are not even talking about campaign promises, although Reagan makes much of his fidelity to them, and his 1980 promises did put heavy stress on building America's defenses to match a growing, global Soviet military threat.

Here we are talking about something nearly evangelical: a profound philosophical conviction that communism is evil, that it takes its guidance, wherever and in whatever form it may appear, from the rulers in Moscow; and that those rulers, whoever they may be at any time, are committed to worldwide ideological conquest.

It's true that those who have known and written about Ronald Reagan the longest always speak of his sensible flexibility on particular programs while he was governor of California. He would bend, or even change his mind, though preferably in a way that maintained at least the appearance of consistency.

But his philosophy on communism and its mortal threat to freedom was written in stone even before he became an active politician. Some say it evolved out of his experience as a trade unionist in the Screen Actors Guild. In any case, the same visceral, impassioned feeling can be found in his public utterances over the last 30 years. It nearly worked in his fight against President Ford in 1976, when d,etente was his favorite target. By the frequency of its use, he obviously thought his soft-on-communism charge against Jimmy Carter was a help.

But there can be no question about the depth of his anti-communist beliefs. He was talking policy, not playing politics, in London last June when he spoke of a "plan and a hope for the long term--the march of freedom and democracy which will leave Marxism-Leninism on the ash heap of history."

Some of the common threads running through the midterm critiques would have us believe that the "disarray" in the Reagan administration derives from the president's submission to manipulation by warring advisers; that only the saving presence of George Shultz at the State Department (and taking a hand in economics as well) offers a hope of a more coherent and consistent performance in the months ahead; but that Reaganism is a fading fancy in any case.

I don't know about that. What does seem certain is that (1) it would require more than mere manipulation to alter the fundamental Reagan philosophy and (2) it would take a fundamental alteration to bring significant changes in his approach to the problems of arms control and defense affecting relations with the Soviet Union.

After two years in office, Ronald Reagan was prepared to say the other day that "I do not believe that philosophically I have changed at all." That figures. If he changed now he couldn't explain it--and be himself