When Manfred Ruehle returned from a business trip one day last June, he decided not to go home but rather to go straight to the school in Weinstadt, near Stuttgart, where his 13-year-old daughter, Stefanie, was to appear in the annual school play.

When he entered the auditorium, he later related, all eyes turned toward him, staring incredulously. Everyone there knew what he did not. A few hours earlier, Stefanie had shot herself to death within minutes after receiving a form letter from her school saying that she would not be promoted from the sixth to the seventh grade.

In the town of Schneittenbach, near Nuermberg, 14-year-old Franz Siegert was feeling pretty good late last June. He had expected to receive one of the dreaded "blue letters" notifying him that he would not be promoted, but it had not come in the mail. When he went to school on the last day, however, his teacher told him it would be coming. Instead of going home, Franz went into the nearby woods and hanged himself.

The deaths of Stafanie and Franz were tragic. But they are hardly unique in West Germany, where 621 youngsters between the ages of 10 and 20 - virtually all of them students - committed suicide in 1976, the last year for which complete official statistics are available.

The number is almost double the figure of 10 years ago. When young people between 20 and 25 are added, it jumps to 1,468. Sociologists estimate that between 7,000 and 14,000 unsuccessful suicide attempts occur here annually.

West Germany - like Finland, Denmark, Austria and Japan - traditionally has had a relatively high suicide rate.But the growth of youth suicides in recent years has become alarming enough to bring this hidden drama of the classroom into the open.

It has provoked relatively small groups of parents around the country to demand a relaxation of stress in schools and has stimulated many sociologists, in turn, to warn that the problem is more likely to be in homes and in the society generally.

"School is rarely to blame," argues West Berlin child specialist Klaus Thomas, "although it often looks as though school is the cause."

Thomas believes that about 40 percent of all youngsters who attempt suicide are suffering from severe and prolonged depression and that about a quarter of the attempts stem from sexual problems. Beyond this, he says, it is society in general and insecurity at home that drive children to suicide.

"The stress in West German schools is higher than in other countries," says Kurt Nitsch, who heads an association in Hannover aimed at preventing child suicides.

More important, he says, is what he calls "the deprivation by parents of more time and love for their children. Too many Germans have forgotten there are children. Too many families have both parents working and too often parents pressure their children to perform well in school.

Hanging over this is what sociologist Helga Gripp and other specialists detect as a certain hostility toward children in some sectors of West German society. It is a mixture, they feel, of young couples not wanting children because they are seen as an obstacle to personal prosperity and older generations tending to treat adolescents, especially, as nuisances.

Nevertheless, to thousands of parents who may have suicide-prone youngsters and who say they love those children, the problem is far more specific and the finger frequently is pointed at the schools.

The path to a respected profession in Germany has always been through the elite system of the gymnasium , a preparatory school and the relatively few universities.

The universities, however, are jammed as a result of trying to open them up to more students in recent years. There are now about 880,000 students in West German universities about five times the level of 20 years ago. There are few if any new universities, however.

Thus, the struggle for high grades on route to the coveted abiter , or the equivalent of the preparatory school diploma, is extremely acute because no longer is the mere winning of the diploma a certain ticket to a university and a respected career.

The generally slow economic growth of the economy also has made job competition fierce at all levels. All of this has contributed to stress and competition in the schools and parental demands to do well.

Psychologist-author Juergen vom Scheidt estimates that 25.30 percent of all west German school children in one way or another are made ill by school and require treatment, which their parents may or may not ask for.

Vom Scheidt points out that many school children - who attend half-days, six days a week - do not have team sports at school to work off some of the tension. The attachment of the school is academic only.

Margit Wesiack, who helped found a citizens' society "for more humanity in the schools in Stuttgart, says the schools are too steeped in" an intellectual education, with too little emphasis on humanities or sociology. Even if those subjects are taught - or even a music course - they are always fliled with theory."

"The cause of the suicide often is deep depression," she argues, "but at times it is triggered by school pressures."

In Stuttgart last week, two groups campaigned for a reduction in the academic workload and were sharply critical of state authorities for allegedly taking no action to combat the youth suicide trend.

Citing school polls, they claimed that one-third of the students feared their parents' displeasure because of their school performance.

The groups urged smaller classes and, most important, greater attention to the training of teachers in handling student's psychological needs and the hiring of trained counselors and psychologists in schools.