Every month the editors of Washington Consumers' Checkbook magazine report here some of the best prices they have found in surveying more than 300 area retailers.

The retailers have promised to hold these prices -- and offer rain checks if supply runs out -- until Aug. 31. It's a good idea to call ahead to check that a product is in stock. Stores may limit purchases to one per customer.

Here's a partial listing of bargain prices based on Washington Consumers' Checkbook magazine surveys. 19-INCH COLOR TELEVISIONS

*Sylvania 19-inch color television, model RXD168WA, electronic tuning, cable ready -- $329 at Twinbrook TV Sales and Service, Rockville (424-8111).

*Sanyo 19-inch color television, model 91C621N, electronic tuning, cable ready, remote control -- $400 at The Stereoman, Arlington (522-5151), Vienna (827-5797).

*Hitachi 19-inch color television, model CT1947, electronic tuning, cable ready, remote control -- $370 at Alco Electronics, Alexandria (780-5180). ANSWERING MACHINES

*Code-A-Phone answering machine, model 2530, voice-activated recording, variable outgoing messages, remote control -- $150 at Telephone Warehouse in the District (333-2600).

*Record-a-Call answering machine, model 675, voice-activated recording of incoming messages, variable outgoing messages, remote control -- $94 at Evans, Rockville (770-6400), Arlington (892-2800), Alexandria (256-6700), Fairfax (425-9000), Manassas (631-2333). EXERCISE BICYCLES

*Monarch Mark II 865 exercise bicycle -- $366 at American Physical Fitness, Rockville (340-0001).

*Tunturi Pro Trainer exercise bicycle -- $459 at College Park Cycles, College Park (864-2211).

*Racer-Mate III exercise bicycle, model 504 -- $105 at Metropolis Bike and Scooter in the District (543-8900). UPRIGHT FREEZERS

*Frigidaire upright freezer, model UFP16A, 15.7-cubic-feet capacity, frost free, adjustable shelves -- $459 at A&A Appliance in the District (723-3315).

*General Electric upright freezer, model CA13DF, 13.3-cubic-feet capacity, adjustable shelves -- $396 at Graeves Tire & Appliance, Wheaton (949-0211).

*Whirlpool upright freezer, model EV150FXR, 15.1-cubic-feet capacity -- $490 at Tanen Sales Co. in the District (783-0395). DISHWASHERS

*General Electric dishwasher, model GSD900D -- $368 at J. R. Enright, Chevy Chase (654-1700).

*Maytag dishwasher, model WU302 -- $469 at Buls Maytag Home Appliance Centers, Rockville (231-0844), Silver Spring (589-3363), Vienna (281-4890), Springfield (644-2977), Alexandria (765-2206).

*Whirlpool dishwasher, model DU5504XM -- $350 at Alco Electronics Inc., Alexandria (780-5180). If you feel a retailer has not met its commitments, Checkbook's editors would like to know. Write: Checkbook, 806 15th St., N.W., Washington, D.C. 20005.