Several Northern Virginia colleges and universities are offering tuition-free courses to residents over 60 years old who have taxable incomes under $5,000 a year.

A wide variety of subjects are offered in credit and non-credit courses.Some of the schools have many openings for seniors while others offer the free education on a first-come, first-served basis after tuition-paying students have been accomodated.

At Northern Virginia Community College a popular course for seniors is automotive engineering, offered at the Alexandria campus, in which students learn to make their own repairs and save money on car maintenance.

Interested seniors are encouraged to call any of the following schools for an application or for more information on classes.

George Mason University. 323-2000. A wide variety of classes is open to seniors.

Northern Virginia Community College. Semester runs Sept. 25 through Dec. 15 for all branches.

Alexandria Campus, 323-4285. A variety of courses including language, art, philosophy, photography, automobile engineering.

Annandale Campus, 323-3000. Basic subjects, plus real estate, nursery, and hotel and restaurant management.

Loudoun County Campus, at Sterling, 323-4558. Basic courses, and specialized classes in borticulture and animal science.

Manassas Campus, (703) 368-0184. Basic subjects. Speciality here is aviation technology.

Woodbridge Campus, (703) 670-2191. Basic courses, plus specialized classes in air conditiining and refrigeration.

University of Virginia, 532-5800. School of Continuing Educations, Falls Church Regional Center. Classes begin week of Sept. 12 and end Jan. 9. Senior citizen's registration for credit classes for Friday, Sept. 9.

Fees for non-credit programs are reduced by 25 per cent for seniors. Those interested these classes are asked to preregister by mail to be assured of spaces in these classes. For further information, please call 532-5800.

Virginia Polytechnic Institute and State University Extension Division, 12100 Sunset Hills Road, Reston, Va. 22090; phone 471-4602. Classes begin Sept. 21 and end Dec. 16. Among non-credit conference classes are Owning and Operation of a Small Business, Animal Control Workshop - Animal and Pet Control, and Seminars in Women's Management. Graduate school: economics, urban affairs, computer science, business administration and home economics.