THIEVES ARE NETTING AT LEAST $2 BILLION A YEAR OUT OF THE 26 BILLION CHECKS WRITTEN BY AMERICANS EVERY YEAR. ALTHOUGH THE MODUS OPERANDI USED BY THESE WHITE COLLAR CRIMINALS ARE VARIED, THEY ALL FIND IT EASY TO PASS BAD CHECKS. CONTRIBUTING TO THE GROWTH IN CHECK FRAUD ARE CARELESS BANK TELLERS WHO HAVE BEEN KNOWN TO CASH ADVERTISING VOUCHERS AND CREDIT DISCLOSURE FORMS STAMPED NONNEGOTIABLE. CHECK ARTISTS, HOWEVER, ARE ADEPT AT OFFERING REASONABLE FACSIMILES OF REAL CHECKS, OR AT STEALING THE REAL CHECKS THEY NEED (WITH BLANK PAYROLL CHECKS AS A PRIME TARGET). SOME CHECK FRAUD ARTISTS OPERATE IN RINGS, WITH CALIFORNIA APPEARING TO BE A FAVORITE HUNTING GROUND FOR THIS TYPE OF CRIMINAL. TO REMEDY THE CURRENTLY BLEAK PROSPECTS FOR DETECTING AND BREAKING THESE FRAUDULENT OPERATIONS, THE MOST PRESSING NEED IS FOR COOPERATION BETWEEN LAW ENFORCEMENT AGENCIES AND PRIVATE INVESTIGATORS WORKING FOR RETAIL FIRMS AND BANKS. THE PRIVACY ACT, WHICH FORBIDS ANY RELEASE OF INFORMATION ABOUT A BANK CUSTOMER'S ACCOUNT WITHOUT A COURT ORDER, IS CRITICIZED AS HINDERING INVESTIGATIONS, AND PROTECTING CRIMINALS INSTEAD OF THE PUBLIC. CASE HISTORIES OF VARIOUS INGENIOUS AND SOPHISTICATED CHECK FRAUD SCHEMES ARE DESCRIBED, INCLUDING ELABORATELY ESTABLISHED FALSE IDENTIFICATIONS, SIGNATURE FORGERIES, OPERATIONS INVOLVING COMPUTER CODING SCHEMES USED ON CHECKS, THE USE OF CHECK WRITING MACHINES TO EMBOSS FIGURES ON CHECKS, AND OTHER VARIATIONS. BANKS ARE TRYING TO DEVISE NEW PROCEDURES AIMED AT THWARTING CHECK FRAUDS, AND POLICE INVESTIGATORS ARE CONSTANTLY UPDATING THEIR DETECTION TECHNIQUES. (LGR)