Dr. Caldicott's remedy for a fevered missile race; Missile Envy, by Dr. Helen Caldicott. New York: William Morrow & Co. 365 pp. $15 .95.

This may well be the most important book published this year. For the subject is the end of the world as we know it. How? By nuclear attack, either launch-on-warning or accidental.

With urgency and high emotion, Dr. Caldicott describes the dilemma, from the days of America's own nuclear preponderance, to parity in the 1970s, to our present quest for superiority. Her formula for the steps to be taken to begin the pullback from the abyss add a dimension of hope to her cry of danger and near-despair.

Caldicott's credentials are medical, her field clinical child care. After an eye-opening trip to Russia and a year of self-searching she resigned from the Harvard Medical School. What actually triggered her decision was the addition of the Pershing II and cruise missiles to the US arsenal, weapons she considered unnecessary to superiority and which dangerously reduced the lead time between accident and disaster.

She then founded Women's Action for Nuclear Disarmament. She appeared, with spectacular success, on many platforms and programs. She wrote a book called ''Nuclear Madness.'' In December of 1982, she met with President Reagan. To her the interview was deeply disturbing, and she has made the rebuttal of his views the leitmotif of her present book.

Very briefly, the President's convictions, as expressed in the 75-minute give-and-take, were these: The Russians are ahead in megatonnage and missiles and killer submarines; a nuclear freeze at the present stage would ''freeze them into a position of superiority.''

When she confessed her nuclear fears, ''the President replied that he, too, doesn't want nuclear war but that our ways differ; he believes in building more bombs.''

The present book is a structured argument against the belief that the US nuclear arsenal is inferior. To Dr. Caldicott, the supposed Soviet lead in missilery is based on the outmoded idea that the weight of the warhead is what counts. She reminds us that American warheads are smaller because the United States has learned the technique of miniaturizing them. The Soviet Union does not possess anything to match the cruise II and Pershing II. ''It does not have an incredibly accurate land-based missile like the MX or a sophisticated, accurate sea-launched missile like the Trident II. But almost certainly it will develop these if the arms race is not stopped.''

On medical matters Dr. Caldicott is more original and sometimes on firmer ground than she is on technical matters. She understands the human element that plays its part in the danger of nuclear accident - the drugs, the boredom of isolated outposts, the feeling of machismo. The title of the book is taken from the area of her competence. ''Missile envy'' is partly the illusion that the bigger weapon is the better. It also touches the macho element in our society: The only way to forestall the enemy is to be bigger and tougher than he is.

So what do we do to reverse the insane spiral of the arms race? ''Missile Envy'' would not be the challenging book it is if it only sounded a warning. Here are five of the six steps Dr. Caldicott believes need to be taken now: (1) a nuclear weapons freeze; (2) a nonintervention treaty signed by the superpowers , which will end military intervention in developing countries and superpower satellites; (3) reduction in the huge NATO and Warsaw Pact conventional forces; (4) an end to the massive international arms trade to third-world countries; (5) a move toward rapid bilateral nuclear disarmament.

I omit the sixth step (''an end to innovation and development of conventional weapons'') from this otherwise pragmatic list simply because it is a hope-too-far, given the macho element Dr. Caldicott herself is so aware of.

This is not a partisan book, for the stakes involved transcend party. What Dr. Caldicott finds terrifying is Reagan's idea of how peace can be achieved. What she questions is the five-year, $1.8 trillion drive for a superiority that she maintains the United States already possesses - a superiority beyond America's need and almost beyond its means.