With most of their schools quiet for the summer, the 450 administrators who run Montgomery County's schools shed their neckties and nylons yesterday, sat in students' desks and concentrated on an issue that is reshaping their jobs: the changing family.

For three hours, principals, curriculum specialists and budget analysts tried to think like social workers. They considered divorce and homelessness, immigrants and ethnic minorities, and parents who are at work while their children are at home.

"I'm very concerned that we really relate to families," said School Superintendent Harry Pitt, who summoned the entire administration of the 102,000-student system to the conference at Quince Orchard High School in Gaithersburg. "Unless the school system can be almost extended family, I don't think we can succeed."

The morning's main attraction was Alvin Poussaint, a noted Harvard psychiatrist who talked about grandparents' effects on children, the cultural symbols in fairy tales, and television.

"Kings, queens, princes and princesses, they all have to do with the nuclear family," said Poussaint, who was paid $5,000 for his hour-long talk and a videotaped question-and-answer session afterward.

As a result, he said, very young children learn stereotypes that may be out of synch with their families and the cultural diversity they will find in school. "There are no Asians in fairy tales and no Latinos in fairy tales."

Poussaint said what children are exposed to is "no longer determined by the family."

"You can grab a 4- or 5-year-old and . . . they can talk about AIDS, they can talk about sex, they can talk about homosexuality . . . . What they . . . are exposed to is no longer determined by the family."

And Poussaint, who has been a script consultant to television's "The Cosby Show," talked about the way children are affected by TV. When young children are reared on "Sesame Street," he said, "They've been told that teachers sing and dance. Then they look at kindergarten and say, 'What is this?' "

After Poussaint's talk, the administrators divided into 15 workshops.

In one room, they considered the county's growing number of poor children. During 1988-89, they learned, children occupied one-fifth of the beds in Montgomery's homeless shelters, and about 400 homeless children attended the county's public schools. Nearly 12,500 Montgomery students -- about 12 percent of the school system -- are poor enough to qualify for federal lunch subsidies.

In another, a Johns Hopkins University researcher dispensed tips for enlisting parents in their children's education. "We have to keep school on the agenda at home, something to talk about apart from 'Did you put the dog's food in the dish,' " said Joyce Epstein, who directs Hopkins's School and Family Connections project.

Schools must try to reach all parents in innovative ways, she said. To coach parents on how to understand report cards and help with homework, she suggested, schools could lend videotapes or set up a telephone system that parents may call for recorded messages. "We must find ways to summarize information in words and languages that parents can understand."

Some principals, she said, have helped to make parents feel welcome by creating a special room for them at school. Then she tested her class. How many already have such rooms, she asked the 18 administrators in the session. Only one principal raised her hand.

"Even here, in great Montgomery County," Epstein said, "there are 70 to 75 percent of parents sitting home and saying. 'I'd like to help my child, but I don't know how.' "