"The most upsetting letters I receive are from schoolchildren who write to me as a class assignment. It's evident they've discussed the most nightmarish aspects of a nuclear holocaust in their classrooms. Their letters are often full of terror. This should not be so . . . Our children should not grow up frightened." --Ronald Reagan

Those comments came last November when the president asked the nation to back his plans for the "absolutely essential" MX missile. Last week, a presidential commission of old soldiers and former defense secretaries agreed: America, to preserve the peace, needs to bolster its arsenal of 9,000 nuclear weapons with 100 MX missiles, each loaded with 10 warheads.

Schoolchildren weren't mentioned in the commission's report. Reagan, presumably, will have to deal with them, since he raised the subject in the first place.

In the Reagan curriculum, talking about the bombs is the problem, not the bombs. Stop the talk, stop the fright. That way, instead of writing letters to the president that upset him, the children will write to thank him for being, in his words, a leader "seeking above all else to keep them safe and at peace."

Presidents routinely blame the media for their troubles. Reagan is the first to blame schoolteachers. Apparently a back-to-basics man, Reagan thinks too many teachers are squandering class time to blab about nukes and what happens to human beings when the bombs explode. But the kids, who have mastered the basics, put two and two together. It's their futures and their bodies that Reagan and his MX commission are threatening with mass burial.

The teachers would gladly keep their students' noses in the textbooks except that the books flunk the test when it comes to accurate information on the nuclear age. In a recent paper, "Militarism in Textbooks: An Analysis," which appeared in the Bulletin of the Council on Interracial Books for Children, Sharon Wigutoff and Sergui Herscovici told of their survey of 11 history books widely used in junior high and high schools:

"The information they present about nuclear weapons and the dangers of nuclear war is inadequate, misleading and irresponsible. At worst, texts avoid reference to nuclear arms completely and concentrate on the use of nuclear power as an energy source. At best, they acknowledge the existence of an arms race and a need for arms limitation, but they uniformly fail to provide the background necessary for informed discussion about the consequences of the arms race, nor do they ever make clear that limiting arms does not eliminate the threat of nuclear war."

The authors are saying that a military-educational complex exists and that the more ignorant students are kept, the easier it is for leaders to sell their plans for war preparation.

This dangerous imbalance is about to shift. The National Education Association and the Union of Concerned Scientists are currently offering a teachers' instructional guide called "Choices: A Unit on Conflict and Nuclear War."

It is a 144-page book developed from field tests in 34 states. The purpose is to provide the young with the information they have been denied too long: the history of nuclear weapons, the consequences of their unimaginable destructiveness and the options available for schoolchildren and all citizens to settle disputes without the nuke button.

The strength of the book is that it offers precise lessons, worksheets and quizzes. Teachers may be in for their own learning experiences. Can they correctly answer No. 4 in the final quiz: "An MX missile is about as powerful as how many Hiroshima bombs? (a) 50, (b) 100, (c) 200, (d) 250." The answer, which won't be found in any Ronald Reagan pro-weapons speech, is (d) 250.

There are sure to be critics who say that the book is designed to raise a new generation of doves. It won't take much for the hard right to move beyond its charges that the freeze movement is a Soviet ploy to scream that now the schools_the prayerless public schools_are administering a pinkish wash to the brains of the young with subversive talk that the arms race is insane.

"Choices" would be stronger if it had a sharper moral tone. Education about nuclear weapons can't be value-free. The choice is inescapably moral: life without nuclear weapons or death with them.

In future editions, the book would be more powerful with a simple appendix: a sampling of letters to the White House from frightened schoolchildren. Reagan has made it clear that he has no use for their fears.