Japan's best seller now in America; Totto-Chan: The Little Girl at the Window, by Tetsuko Kuroyanagi, translated by Dorothy Britton, illustrations by Chihiro Iwasaki. New York: Kodansha International. 195 pp. $9.95.

It's not hard to account for the popularity of this slim memoir with Japanese children and their parents. In a land where societal pressures are great for getting into the ''right'' schools - beginning with kindergarten - one graduate has come forward to show that there can be some enchanting alternatives.

Tetsuko Kuroyanagi, a talk-show personality, pays tribute here to the headmaster and founder of the unusual elementary school she attended in the early 1940s. In his attempts to uncover and develop the ''good nature'' of every child in his charge, Sosaku Kobayashi took some daring steps: He taught boys to respect and be nice to girls, helped his students to understand their classmates' physical handicaps, encouraged them to enjoy conversation with their meals, and was actually known to listen to their concerns.

Although the school's physical setting might have been considered bizarre by some (classes were held in abandoned railroad cars, and an antiquated fish pond served as swimming pool), the spirit that pervaded the campus was as fresh as the spring breezes that blew through the surrounding cherry trees. In addition to their daily lessons, the 50 students learned how to camp by pitching tents in the Assembly Hall, learned how to cook rice and pork soup by carrying pots along on school outings, and even learned how to help put food on the family dinner table by winning vegetables for prizes at the annual sports days.

The incidents recounted here really happened, says author Kuroyanagi, and she retells them with charming wit and occasional wistfulness. Expelled from her first elementary school for daydreaming and for talking to street musicians and swallows from her ground-floor classroom, she says she could have become a confused and complex-ridden child, were it not for one of her headmaster's constant reminders. ''You're really a good girl, you know,'' he used to tell her , and that faith in her innate goodness has continued to carry her through some formidable adult challenges.

After breaking all publishing records in Japan, ''Totto-Chan'' can be expected to attract American educators, parents, and perhaps even some children who appreciate the international view beyond their own first-floor windows.