Fairfax County residents may have their auto emission systems tested free of charge from now through October. The program, started by the county Health Department's Air Pollution Control Division in cooperation with the Public Library system, is part of an effort to control air pollution in the county.

The testing, which takes about three minutes, can alert car owners to the need for adjustments and repairs that will reduce harmful emissions and imrpove fuel economy.

Emission testing sites will and open from 10 a.m. to 3 p.m. at the following locations.

Dolley Madison Library, 1244 Oak Ridge Ave., McLean, Oct. 17; Fort Belvoir, 12th and Belvoir Rd. (behind the main PX), Aug. 28; George Mason Regional Library, 7001 Little River Tpke., Annandale, Oct. 10, John Marshall Library, 6209 Rose Hill Drive, Franconia, Sept. 19; Massey Building, 4100 Chain Bridge Rd., Fairfax, Sept. 26.

Patrick Henry Library, 101 Maple Ave., Vienna, Aug. 22; Richard Byrd Library, 6400 Cumberland Ave., Springfield, Sept. 11; Sherwood Regional Library, 2501 Sherwood Hall Lane, Mt. Vernon, Oct. 3, and Thomas Jefferson Library, 7415 Arlington Blvd. (near Loehman's Plaza), Aug. 15 and Oct. 23.

For more information call the Air Pollution Control Division at 691-2541.