Southland Corp., parent Company of the familiar 6,805 7-Elevens around the United States and Canada, started paying attention about five years ago to what a hardened ex-convict had to say.

On the convict's advice, hidden cameras were discarded, silent alarms disconnected and secret mirrors removed. All security devices were brought in plain view.

It sounded like a set-up.

And it was.

The Southland Corp. was taking a risk that the suggestions of Ray Johnson, experienced specialty store hold-up man and former ex-convict, would help stem the tide of convenience store robberies the chain had been suffering since 1973.

"No one can tell you more about crime than a hardened criminal," Johnson said.He should know, claiming nearly two score heists and having spent about 2 1/2 decades behind bars, including five years in solitary confinement.

Johnson soon demonstrated to Southland officials that not hiding security was the surest way to reduce robberies in 7-Eleven stores. His theory was based on visibility -- demostrate to the potential robber his risks before the crime was committed in hopes of showing the crime would not work.

The 7-Eleven stores began to acquire a new look. The once ubiquitous posters and display advertising that cluttered storefronts gave way to a neat, open appearance. Store aisles, previously aligned according to the whims of the store designer, were arranged to allow an unobstructed view of the cash register area from the street.

And the amount of money kept on hand to operate most 7-Elevens dropped during daytime hours from about $250 to about $60. After dark that figure drops even farther, to about $20, in small change.

The heart of the new nighttime approach is the Tidel Systems "Tacc --1" timed access cash controller system.

The theory behind the Tacc-1 is simple. During evening hours, a 7-Eleven cashier keeps only enough change in the cash register to cover a small purchases made with a $20 bill. In the event more change is needed, a button on the Tacc-1 will release an additional $10 in small bills and change at random intervals of 10 seconds to two minutes each time the device is activated. The cashier can't controll the amount of time necessary for the drawer to yield additional change, nor does he have a key to the bullet-proof cash reservior in its bottom. A slot on the top allows nonretrievable desposits during the course of an evening.

"Two minutes is an eternity to a scared man with a gun in his hand," said Johnson. And the Small amount of cash kept on hand by the cashier to conduct normal business is not much of an enticement to a would-be armed robber.

The system has yielded gratifying results not only for Southland Corp., but for 7-Eleven employes as well. In the past five years, the convenience stores have recorded a 30 percent drop in armed robberies.

Those hold-ups that have occurred have resulted in 50 percent less related violence against cashiers and store employes. "Violence-avoidance" training for Southland's 7-Eleven employes aims at creating cashier behavior "more appropriate during a crime."

The employes themselves are trained to treat robbers "just as you would any other customer," said Johnson , and this politeness and cooperation itself has foiled more than one hold-up attempt.

Other changes in the stores themselves have also increased the risk for would-be gunmen. Most 7-Eleven entrances have tape measurers affixed to the door frames to help clerks estimate a robber's height. Store personnel are trained in handgun recognition and are provided with duplicate-copy profile sheets that facilitate future identifications and are an invaluable aid to police when correctly filled out.

A new program initiated at some 7-Eleven involves taxi drivers and policemen taking their rest and coffee breaks in store parking lots. In return for an occasional pastry or hot beverage, these drivers keep an eye on the shop during their regular rounds each time a fare or patrol takes them past the window.

Johnson has helped in all these changes, and the results for 7-Eleven have been worth the gamble.

It's paid off.