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 June 30. It is a good idea to call ahead to check that a product is in stock. Explain to the retailer that 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 the magazine's survey. 12-SPEED BICYCLES

Royce Union 12 speed bicycle, model 8179-3 -- $140 at Lanham Bicycle & Turf, Lanham (577-9763).

Bridgestone 12 speed bicycle, model 300 -- $200 at Lanham Bicycle & Turf, Lanham (577-9763).

Raleigh 12 speed bicycle, model Pursuit -- $205 at Griffin Cycle, Inc., Bethesda (656-6188), Silver Spring (384-2111).

Schwinn 12 speed bicycle, model Worldsport -- $210 at Chevy Chase Bicycle in the District (966-2705).

Schwinn 12 speed bicycle, model Traveler -- $240 at Chevy Chase Bicycle in the District (966-2705).

Trek 12 speed bicycle, model 400 -- $299 at College Park Cycles, College Park (864-2211). MATTRESSES

Sealy queen-size mattress with matching boxspring, model Imperial -- $309 at Custom Bedding Co., Cottage City (699-1330).

Serta queen-size mattress with matching boxspring, model Adventure -- $386 at The Bedstead, Springfield (569-0553).

Simmons queen-size mattress with matching boxspring, model Monarch -- $479 at Denis Sleep Shop, Langley Park (434-0336). COLOR TELEVISIONS

Zenith 19" color television, model SB1965W, quartz tuning, 178-channel cable ready, MTS stereo sound, wireless remote control -- $420 at Paul's Audio Video Center, Vienna (827-5797) and The Stereo Man, Arlington (522-5151).

Toshiba 20" color television, model CX2045, electronic tuning, 117-channel cable ready, wireless remote control -- $439 at Twinbrook TV, Inc., Rockville (424-8111).

Sony 19" color television, model KV1981R, quartz tuning, 181-channel cable ready, built-in stereo decoder, wireless remote control -- $599 at Nuri's TV & Video Center, Falls Church (560-0707). VIDEO CASSETTE RECORDERS

Toshiba video cassette recorder, model M5100, VHS format, wireless remote control, 7 day/1 event timer, 117-channel cable compatible, voltage synthesized tuning -- $269 at Twinbrook TV Inc., Rockville (424-8111).

RCA video cassette recorder, model VMT385, VHS format, wireless remote control, 14 day/4 event timer, 117-channel cable compatible, high quality sound, auto rewind, electronic tuning -- $375 at Alco Electronics, Inc., Alexandria (780-5180).

Fisher video cassette recorder, model FVH960, VHS format, wireless remote control, 14 day/9 event timer, 140-channel cable compatible, high quality sound, built-in stereo decoder, quartz tuning -- $749 at Paul's Audio Video Center, Vienna (827-5795), and The Stereo Man, Arlington (522-5151). 35MM SINGLE LENS REFLEX CAMERAS

Konica 35mm SLR camera, model FC-1, fully automatic or manual operation, shutter priority -- $180 at District Camera Shop in the District (393-6585) and Embassy Camera Center in the District (483-7448).

Contax 35mm SLR camera, model 159MM, fully automatic and manual operations, program aperture priority -- $466 at Pro Photo in the District (223-1292). 35MM COMPACT CAMERAS

Olympus 35mm compact camera, model XA, manual focus -- $115 at Conn Camera & HiFi in the District (293-5484).

Pentax 35mm compact camera, model Super Sport 35, automatic focus -- $140 at Pro Photo in the District (223-1292).

Nikon 35mm compact camera, model L35AF, automatic focus -- $140 at Penn Camera Exchange, Inc. in the District (347-5777).

Yashica 35mm compact camera, model T-AF, automatic focus -- $150 at District Camera Shop in the District (393-6585) and Embassy Camera Center in the District (483-7448).

If you feel a retailer has not met its commitments, or if you would like to know more about Checkbook's survey, call (202) 347-7283.