What did you say you were doing this weekend?

From George Washington at Valley Forge to the shopping malls of Indianapolis, adult education has come a long way. General Washington's tutors taught the troops to read and write right on the battleground. Today, Indiana and Purdue professors teach algebra and literature at Sears and Penney's.

This may be the fastest-growing innovation in higher education: the weekend college. It lures degree-minded workers too tired for night classes, or too busy with irregular job or family schedules.

Weekend college requires attendance on two or three days of the weekend, usually two weekends a month.

Across the United States, college students seem to be going for it. Miami Dade Junior College had a weekend program as early as 1966. But it's the last few years that the pace has picked up.

Since 1977, nine weekend colleges have formed in Ohio alone. Alverno College in Milwaukee has tripled its weekend college enrollment since its start-up roster of 244 in 1977. The movement now makes possible associates, bachelors, and master's degrees by attending classes only on weekends.

Adults are swelling student ranks. There are now more than 1 million students older than 35. Women, making up 60 percent of this older student population, have become the new majority on college campuses.

Educators attribute this rush back to school to several factors including: (a) new awareness for lifelong education and personal growth; (b) more leisure time; (c) new careers and opportunities for women; and (d) midlife career reassessments for men who question their present job satisfaction.

Rapid technological changes have prodded people back to school to keep pace in a more competitive job market. An official of a pioneering weekend college has suggested that a skilled professional out of school for 10 years is also probably out of date.

James Bliss, 47, a student at Kent State University, feels himself ''moving into a more technical, computerized era.'' He reasons that, ''Given a choice of someone with a degree and one without, business will hire the person with the degree.''

There are an estimated 40 million adults in career transition. According to the College Board, some 25 million of these will seriously consider enrolling in college in the next 10 years.

The vast adult enrollment might be defusing a crisis that has been confronting many colleges and universities. The number of younger students has dwindled fast.

In their efforts to win the new student population, schools are making it easy to enroll, fitting the courses to the students' personal schedules, and making serious attempts to keep them in school.

For example, the C. W. Post Center/Long Island University, which has some 1, 800 to 2,300 students per session, offers family rates for weekend college, shuttle buses from nearby railroad stations, and a creative arts program for the children of weekend college students given at a nearby school.

Weekend college students generally seek business or liberal arts degrees. Most programs can be completed in four or five years.

Administrators consistently depict weekend college students as self-motivated and committed to hard work. Students present a contrary image. ''Some people seem to think that going to weekend college is easy, that it isn't quite like 'real' college. In fact, I have had to tell people I wasn't spending the weekend taking ceramics,'' said Karen Clyde, who's doing her studying at Ohio's Hiram College.

Employer support is important for weekend college students. Many say that without it they would not be able to attend. The colleges report that 40 to 85 percent of the students in the weekend programs get financial help from their employers.

The academic quality of weekend colleges remains to be documented. As of this summer, Howell McGee, past executive vice-president of the Association for Continuing Higher Education, reports that the weekend college concept has not yet been formally evaluated. Educators are curious about everything from tuition-pricing structures and the quality of teaching staffs to the ability to retain information given in big but infrequent doses.