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 rainchecks if supply runs out -- until March 31. Call ahead to check that a product is in stock and tell the retailer you want the price quoted in "Checkbook Bargains." Stores may limit purchases to one per customer.

Here's a partial listing of bargain prices based on Checkbook's survey: COLOR TELEVISIONS

Toshiba 20" color television, model CF2015, 117-channel, cable compatibility, electronic tuning, remote control -- $339 at Twinbrook TV Inc., Rockville (424-8111).

Sony 19" color television, model KV-1976R, 181-channel, cable compatibility, quartz tuning, remote control, stereo-compatible -- $439 at Shaffer TV, Inc., Vienna (938-6577). COMPUTER MONITORS

NEC 12" monitor, model JB1260, green screen -- $75 at The College Store, Takoma Park (891-4096).

Amdek 12" monitor, model 300G, green screen -- $125 at Operant Systems, Langley Park (434-0405).

IBM 12" monitor, model COLOR, color screen -- $496 at Frederick Computer Products, Frederick (694-8884). EXERCISE BICYCLES

Vitamaster exercise cycle, model Hide-A-Cycle, portable, speedometer, odometer -- $150 at Evans Distributors & Jewelers, Rockville (770-6400), Laurel (725-6200), Arlington (892-2800), Alexandria (256-6700), Fairfax (425-9000), Manassas (631-2333).

Ross exercise cycle, model Regency 90513, speedometer, odometer, timer -- $249 at Griffin Cycle, Inc., Bethesda (656-6188), Silver Spring (384-2111). Monark exercise cycle, model Mark II 865, full circumference belt tensioner, speedometer, odometer, timer -- $379 at College Park Cycles, College Park (864-2211). CASSETTE DECKS

Technics double cassette deck, model RSB11W, Dolby B noise reduction -- $109 at Evans Distributors & Jewelers, Rockville (770-6400), Laurel (725-6200), Arlington (892-2800), Alexandria (256-6700), Fairfax (425-9000), Manassas (631-2333).

Yamaha cassette deck, model K420, Dolby B&C noise reduction, auto reverse -- $233 at Audio Associates, Laurel (953-7242), Langley Park (434-4740), Arlington (525-1889), Rockville (762-3701), Springfield (971-1060).

Aiwa double cassette deck, model ADWX220U, Dolby B&C noise reduction -- $448 at Audio Buys, Bailey's Crossroads (578-3033), Gaithersburg (840-9180). POWER LAWN MOWERS

Toro power lawn mower, model 16585, side bag, 4.0 horsepower -- $261 at Lane's Lawn Mower Service, Arlington (533-0770).

Snapper power lawn mower, model 2135IPS, self-propelled, rear bag, 4.0 horsepower -- $389 at Kohler Equipment, Landover (577-8111), and South Potomac Lawn Mowers, Fort Washington (292-4444).

Lawnboy power mower, model 8125, self-propelled, side bag, 4.0 horsepower -- $425 at Maryland Cycle & Equipment, College Park (474-6723). QUEEN SIZE MATTRESSES/ MATCHING BOXSPRINGS

Serta Limited queen size mattress, matching boxspring -- $279 at The Bedstead, Springfield (569-0553).

Sealy Carlisle queen size mattress, matching boxspring -- $379 at Custom Bedding Co., Cottage City (699-1330).

Simmons Monarch queen size mattress, matching boxspring -- $479 at Denis Sleep Shop, Langley Park (434-0334). RADIAL TIRES

Pirelli radial tire, model P4, size 165R13, mounted and balanced -- $38 at Radial Tire Co., Silver Spring (585-2740).

BF Goodrich radial tire, model Lifesaver XLM, size 185/80R13, whitewall, mounted and balanced -- $49 at Graeves Tire & Appliance, Wheaton (949-0211).

Michelin radial tire, model XA4, size 195/75R14, whitewall, mounted and balanced -- $70 at D&G Discount Tire Center, Waldorf (843-6343), Mechanicsville (274-3150), Lexington Park (274-3766), Prince Frederick (855-1545), Clinton (868-3411), Forestville (420-3705). REFRIGERATOR/FREEZERS

Whirlpool refrigerator/freezer, model ET17HKIM, 12.45 cu. ft. refrigerator capacity, 4.75 cu. ft. freezer capacity -- $598 at Alco Electronics, Inc., Alexandria (780-5180).

White-Westinghouse refrigerator/freezer, model RS192G, 12.2 cu. ft. refrigerator capacity, 6.8 freezer capacity -- $699 at A&A Appliance Co. in the District (723-3315).

General Electric refrigerator/freezer, model TFX24EF, 14.93 cu. ft. refrigerator capacity, 8.57 cu. ft. freezer capacity, ice-maker -- $1,397 at J.R. Enright Co., Chevy Chase (654-1700).

If you feel a retailer has not met its commitments, Checkbook's editors would like to know. Write: Checkbook, 806 15th St., NW, Washington D.C. 20005.