Many of the millions of children who were primed for Mrs. McAuliffe's lesson from space had a crushing disappointment. Typical of the reactions was that of Becky Carlton, a 6-year-old member of the Young Astronauts in Tucson, Ariz.

As part of a group letter Becky wrote, ''I feel real sad and I want to cry for all the kids and their parents and especially for the teacher because she was the only one who knew, really knew about space equipment and space stuff to teach us.''

For those children who had been looking forward to the lesson from space, Dr. Blinder said the explosion ''stirs up a special frustration, that of a promise broken.'' Psychological Distance

Since the death of the astronauts was at a psychological distance, it seems to have freed many children to pour out their feelings in letters.

Edward Podvoll, a psychiatrist in Boulder, Colo, said: ''It's like the trial death of a parent. They don't feel the emotional paralysis or the anger at being abandoned that can typically well up when a parent dies.''

Kateri Rowe, a student at Our Lady of Perpetual Help School in Lindenhurst, L.I., sent this poem to the McAuliffe family:

Christa McAuliffe excited as could be Got on to the shuttle with no maybe So they counted down and left the pad In one splet second happy turned to sad. We can't beleave it they all said And for that day no one could get it out of their head.

In a postscript, Kateri added, ''I don't know if the poem will help but I feel afull and the poem was the only way I could express myself.''