Ten years ago, Sandra Bremer was toiling over her dining-room table putting together a catalogue offering 24 classes taught by eight teachers.

Last month, Open University, with a March/April catalogue boasting more than 500 courses, 200 teachers and with registrations running about 40,000 a year, sold for "something under $500,000."

"Open U.," says Bremer, 39, really has changed. When I did that first catalogue, it was a little business out of my apartment. Now it's this big thing. Over the last 10 years we've probably had around 200,000 registrations."

The former Peace Corps volunteer was working as a secretary for a media brokerage firm in Washington when her friend Alex Fraser came up with the idea for Open U. As he moved ahead with plans, investor-author-teacher Fraser (an "interdisciplinary miscellaneologist about the same age as Paul Newman and John Derek") decided he really wanted to teach at Open U., which he still does, rather than get caught up in the organizational and operational details.

No one had tried anything like Open University in Washington before, so there was no model to follow. Bremer felt "underemployed" in her job and excited by the Open U. concept: Classes would be inexpensive ($4 and up) and usually given in the teachers' homes. In a sense, Open University and Washington, D.C., would be one and the same. (Today, classes still are held at teachers' homes, as well as at Open U. and in public spaces in the area.)

"I always was the organizer," says the Minnesota native. "I was the high-school cheerleader. I had all this energy. I called around to all the teachers. Lots of them said they loved the concept, that they would love to take the classes but didn't want to teach."

By January 1975, Bremer was working mornings, nights and weekends on Open U. as well as holding down her full-time secretarial job. "I don't know where my mind was. I was so intent on getting that first catalogue out. The first one was painful, then it really became a passion with me."

Bremer agreed to repay Fraser the money he had put into Open U. -- $1,200 or $1,300 for expenses -- within 12 to 18 months. The agreement was that if she never made enough money to repay him, she would give back Open U. to him. "My theory," says Bremer, "was 'If it can't be supported by class fees, then we're not providing a service the people want.' It had to do that and it had to support me within a year."

By Jan. 1, 1976, Open U. was a healthy, growing business. Bremer quit her secretarial job and worked full-time on building up the center. "I don't have any idea how much we made that first year, but we always were in the black. We always paid the bills from Day One.

"We printed 4,000 catalogues. I remember the day I picked them up from the printer. They lent me a dolly to take them back to my office." Bremer handed out catalogues everywhere she went, even on dates.

"I'd give catalogues to the teachers and they'd hand them out. I'd go to the store, the library, everywhere. Pretty soon two things happened: Registration money started coming in and I realized I had to do a May/June catalogue."

Bremer capped her 10-year stewardship with a March/April 1985, printing of 230,000 catalogues and the sale Feb. 20 of Open University to the New York-based Learning Annex.

"It's time," says Bremer, "for me to go on and do something else. The only real decision I've made is that I won't make any decision about what I'll do until this fall. I'm going to take a sabbatical this summer, go hike in the Alps, learn to fly an airplane, learn French in Paris . . .

"I feel love for Open University and it's still a passion for me. I want to remember it that way. I wanted it to be that way for me when I leave."