You are the principal of the alternative Parkmont School in McLean, which would like to move to Washington to be near the resources of the city. But since the school doesn't have much money, the move appears unlikely.

But on Thursday, you are opening your mail, and in it you discover a letter with an unsolicited check for $100,000 to go toward Parkmont's building fund.

You think perhaps someone is playing an elaborate joke, but then the check, from the Minnesopolis Foundation in Minnesota, clears Parkmont suddenly has a $100,000 endowment.

This is what happned to Alex J. Packer, principal of Parkmont, a private junior high school that tries to offer its students a variety of learning experiences, not all of them limited to nornal academic activities.

"We're thrilled," Packer said. "We were beginning to get frustrated . . It's difficult to raise money."

Packer said the school has been trying to find a new location in Northwest Washington, but has been stymied by the high price for suitable quarters "The grant will really make a difference," he said.

Thomas Beach, associate director of the Minneapolis Foundation in Minneapolis, said in a telephone interview the grant was designated for Parkmont by an anonymous donor. Asked why the donor chose the foundation, which primarily funds projects in the Minneapolis area, Beach said, "I honestly don't know the answer."

Parkmont, now located at 16670 Chain Bridge Rd., was founded five years ago and has an enrollment of 55 students from throughout the metropolitan area.

Principal Packer said the student body is "purposely varied. We have students who would be called gifted, some with learning disabilities, students who love school and students who hate school. What they all have in common is that they are extraordinarly happy here."

Packer said students "spend a lot of time on social issue." But at the same time, he said, standardized test scores show the students do well academically compared with other students at other schools.

Parkmont is a cooperative, which means the students' parents volunteer their services, including working as teachers.