The sale last month of Washington's Open University to The Learning Annex, a New York-based chain operation, comes at a time when noncredit adult education is turning into big business.

Some people are even likening the trend to the fast-food industry: speedy consumption, rapid turnover of customers, standardized menus, franchises and high-profit potential.

The education programs -- part of the free university movement of the 1960s -- are, of course, nothing new. What is new, says William Draves, national coordinator of the National Learning Network, Manhattan, Kans., is the rapid growth of for-profit programs. "I think there are two reasons for this: Knowledge in short bits and pieces is almost a necessity for people in their work and in their leisure time. And second, it's a very social experience."

Says William Zanker, 30, founder and chief executive officer of The Learning Annex, which along with Washington and New York, also has operations in Chicago, Atlanta and Houston and plans to open several "outlets" in California: "We're living in the informational age. People need more and more information and they need it quickly. They can't afford to go to these long programs."

Zanker's major competition is Robert K. Wagner, 36, founder and head of The Discovery Center in Chicago, the most profitable noncredit adult learning center in the country. According to Wagner, the program, which has branch operations in Cincinnati and New York, should gross "over $3 million in 1985."

Draves, whose 10-year-old Learning Resources Network tracks trends in adult learning and helps newcomers enter the field, says he's been expecting the emergence of chain operations. "A couple of years ago two or three people said they wanted to become the McDonald's of adult learning and set up branches or franchises around the country."

Zanker and Wagner are trying to do just that. Both stress, however, that national success is dependent on local people being in charge.

"We like to keep local people running our local units," says Wagner, "and that's the way we develop our management. We anticipate bringing in some better ways of doing business, cost savings, advertising know-how, marketing changes."

Schools acquired by The Learning Annex, says Zanker, "become more effective. We bring in computers, get rid of some of the paperwork. But the student won't notice any difference."

Open University, for example, "is an institution in Washington, a household word. That's why we were attracted to it. The basic philosophy stays the same. It would be stupid on our part to change something that's working so beautifully. You only fix stuff that's broken."

Most of the nation's for-profit learning centers are similar: Courses tend to be one-class-only, lasting 1 1/2-3 hours, or one night a week for a few weeks.

Fees are competitive in various cities, with Washington running a little less than Chicago or New York. Open University fees are $10-$65, with several in the $12-$16 range. First Class, which opened in January, charges $8-$45 per course, with several at $10-$15. At the Learning Works, Bethesda, courses are $15-$145, with several at $20-$50.

A sampling of courses from the area centers: "How to be Single and Jewish in Washington . . . And Not Have Your Mother Worry," "How to Marry Money," "Juggling Is Catching," "How to Live With Your Dog," "Leave a Message at the Tone," "How to Live and Feel Like a Millionaire," "Parrot Psychology" and "How to Wear Your Face."

Most learning centers have courses on how to buy a house, dealing with anxiety, starting your own business, tax shelters and other concerns of the day. Draves says the hot topic now is "the liberal arts, specifically centered around foreign travel and foreign cultures."

Trends, he says, "with the exception of sports," do not tend to be geographic. "Something that's hot in Arlington is likely to be hot in Wyoming. When stress and stress management were big, you found them in rural areas even in Wyoming."

Zanker is banking on the fact that what plays in Peoria will play anywhere else. He went public with The Learning Annex in August. "We took in $3.3 million for a third of the company . . . We have an operating system in place, computerization and everything, and we're taking this public money and we're going to pop it out all over the place."

That includes a line of Learning Annex books, put out by Berkley Publishing (64 pages each, $2.95). "It's a series," says Zanker, "just like our courses -- quick and inexpensive." Among titles: How to Cook a Gourmet Meal in 15 Minutes, Success Now -- Why Wait!, How to Win on the Telephone.

"Now we're coming out with videotapes on the same subjects that have been successful as courses and books. We see it as really big business. Basically we're marketers. We've taken a concept that has been around for years and we've learned how to market it."

"Lifelong learning is becoming such a part of our daily lives," says Draves, "that the market has not been saturated. We have not seen a community that has too many learning opportunities."

"No one has determined how small a city can become before it's no longer viable for two competitors," says Discovery Center's Wagner. "I'd just as soon the competition wasn't there. I believe we're going to see a major competitor in every city that we're in. The local programs are going to have a harder time staying independent, in the face of large, national competitors."

Local entrepreneurs, says Zanker, will find it "very hard to compete with a public company like us. Also, if somebody's not computerized in this business, it's impossible. We had been in Open University for only a week and we already installed our computer system.

"We think the Washington market probably is going to be the biggest in the country. It has the right demographics and Open U. has a tremendous reputation."

Says Wagner, his major national rival: "We'd like to go into the Washington area, and we anticipate that we will."