After six hours of competition in June, 12-year-old Katrin Raptakis was ecstatic about winning a place on the pompon team at the Montgomery County junior high school she expected to attend this fall.

Katrin hoped the pompon team would make the shift from elementary school to junior high school a little less intimidating. Now she'll never know. Her hopes for a seventh grade year at Sligo Intermediate in Silver Spring were abruptly shelved by a late night county school board decision July 28 to shift 91 students, most of them white, from Sligo to Eastern Intermediate two miles away.

County board members blamed the decision on a ruling by the Maryland Board of Education, which said the county board had violated its own racial balance guidelines by sending too many minority students to Eastern Intermediate.

The state board, on the other hand, indicated that the county board should have had better planning. The arguments don't really matter to families caught in the middle who are scrambling to prepare their children for a new school with only 19 days left before the start of the new term.

The Sligo-Eastern change is only one of many prompted by the county board's decision last fall to close 28 schools by 1984, largely because of declining enrollment. Each year, the county school district undergoes some pupil reassignment, but never on this scale. About 5,700 students will be moved to new schools this September, school officials estimate, because of closings, attendance boundary changes and grade reorganization.

The students shifted to Eastern only recently completed preparation for Sligo.

"This makes no sense," said Katrin. "After going through a week of orientation for Sligo, now I have to go through orientation again, for Eastern." She can't try out for Eastern's pompon squad, she said, because its members have already been chosen.

The 91 students being transferred come from the Pine Crest and Forest Knolls Elementary schools in Silver Spring and the area around Four Corners Elementary, which closed in June. School system officials say about 70 will have to be bused to Eastern. That decision has wrecked the plans of some parents.

"You never know what is going to happen from moment to moment," said Katrin's father, Steve Raptakis. Her mother, Evi, said the family considered trying to keep her at Sligo by saying she lived in a second house the family owns that is much closer to Sligo. "These are the things they make you think of doing," said Raptakis.

Eleven-year-old Steve Gunther had balked for months about going to Sligo, since most of his friends were going to Eastern. But his parents worked on him, and a week of orientation at the school changed his mind. Now, having decided that Sligo might not be so bad after all, he will go to Eastern.

"I got to like Sligo and now I don't want to go to Eastern. I haven't even been inside that building," said Steve, who dislikes the thought of being bused.

His mother, Susan Gunther, is a consultant, his father a physicist, and both parents often work late and travel. They had decided on an arrangement in which Steve would go to the home of a friend near Sligo when his parents couldn't get home early.

"I am extremely concerned about whether we can find another arrangement on such short notice," said Susan Gunther.

Eleven-year-old Rachel Bayard comes from a single-parent home with four children. Her mother, Susan, describes her as a child who "needs a lot of preparation for new situations . . . in her mind, she has been going to Sligo for the past few months, but every day she would ask, 'Do you know yet what school I am going to?' "

Rachel was familiar with Sligo because two sisters went there. Her sister Lauren still attends Sligo and Rachel felt that would make the transition easier.

"I think they school board members are stupid. I have no idea why I am going to Eastern," said Rachel. "I could walk to Sligo. They should put kids where they live and save the money from busing."

"It kind of isn't fair," said Jennifer Andruzzi, 11, a Forest Knolls graduate who must repeat the orientation session for Eastern that she completed for Sligo. "I won't be able to walk to school unless they build a college here."

Some of the Pine Crest children wanted to attend Eastern all along and are happy about the latest school board decision. Others said they could have adjusted to either alternative. And in a few cases, the children seem to be adjusting better than their parents.

Eleven-year-old Hugh Wooden was pleased. "I have a lot of friends who live near Eastern and I have very few friends who would be going to Sligo," he said.

But his father, William Wooden, an orbital analyst for the Defense Mapping Agency, was irritated when Hugh was switched back to Eastern.

"I don't like having my kid yanked around," he said.