Because Chicago Tribune columnist Bob Greene wrote what he considers "a little, silly throwaway column" earlier this year, you can now have "a chocolate fix" and be faithful to your diet.

Two years ago, Greene lost 22 pounds. "Losing the weight wasn't hard, " he acknowledges. But keeping it off was a challenge. His biggest problem: Greene, "like any sane person," he says, loves chocolate.

Last August, Greene stumbled upon low-calorie Canfield's Diet Chocolate Fudge Soda and remembers thinking that it sounded "pretty weird." The caffeine-, sugar-, saccharin- and sodium-free product, which also contains no chocolate, has only two calories to a 12-ounce can. "I figured it would be horrible," he says, "but when I tasted it, it was great. Taking a sip of the stuff cold is like biting into a hot fudge sundae."

Then, in January, an important story that he was working on for his Sunday column fell through. So, hoping he wouldn't be "too embarrassed," he tossed off "a pretty silly" column about how the Canfield beverage helped him maintain his weight.

Greene wrote that when mild cravings for chocolate occur, he can usually banish them with a gulp of the drink. But when the craving for brownies or German chocolate cake becomes intense, Greene puts the high-calorie sweet on a plate, stares at it for less than a minute, then before "lunging at the cake or cookies," grabs a can of the diet chocolate fudge soda and "takes a swig" while looking at the dessert. Afterward, he wrote, he feels just as satisifed as if he had actually eaten the forbidden sweets.

"It was not a piece," he says, "that you'd think people would give a second thought to."

They did, though, and as a result of the buying frenzy that followed, Canfield's Diet Chocolate Fudge Soda is starting to appear in the Washington area. It is available at Magruders Grocery Inc., Katz Kosher Super Market in Rockville, Sniders Super Market in Silver Spring, can be special ordered by the case through Giant supermarket managers and will be distributed by Joyce Beverages of Forestville.

In the 90-day period after the column, syndicated to 200 newspapers nationwide, appeared, more than 25 millions cans were purchased. Only 1 million cans of the fudge soda were sold during all of 1984 in Illinois, Indiana, Iowa, Wisconsin, Michigan and Kansas City, until recently the Chicago-based A.J. Canfield Company's entire marketing area.

Because many consumers in those areas rushed to the store and bought entire cases (each containing 24 cans), a lot of other people couldn't find the product. Some called Greene to ask if the column was a satire. "They thought I had invented this soft drink that tasted like chocolate fudge but with virtually no calories."

Greene reassured his callers that the soda existed. But when he tried to replenish his own supply, the shortage affected him, too. All the stores where he usually shopped were out of it; caught off guard, the Canfield factory couldn't pump it out fast enough to meet the demand.

The company was bombarded with as many as 500 phone calls a day from supermarket chains and consumers. The factory began around-the-clock production, two 10-hour work shifts every day, which had to be cut back to a six-day work week because of employe fatigue. Greene says he recently got a phone call from a Canfield truck driver who told him, "You've just paid for my house with all the overtime."

In areas of the country where Canfield's product was not marketed, dieting chocoholics who had read Greene's column inundated shopkeepers with requests to carry the item. To appease customers, some of these besieged grocers sent huge trailer trucks, which hold 2,200 cases of soda, to Canfield's main plant in Chicago. When the trucks returned, to prevent hoarding some grocers put a limit of one case to a customer.

On a smaller note, the owner of a little delicatessen that recently opened in Worthington, Ohio, drove to Chicago and packed his van with 100 cases. Word of his trip leaked out. When he returned, a line of chocoholics was waiting. Local media covered the event. Nearly all of the soda sold within 24 hours.

A Sioux City, Iowa, newspaper held a Canfield's Diet Chocolate Fudge Soda contest. Contestants explained why they needed the one and only can of the soda in the city. The coveted can was won by a 55-year-old woman who wanted to lose more weight before leaving for her dream trip to Hawaii.

Back in Chicago, Alan Canfield, senior vice president of the 51-year-old family-owned company, says one of its drivers who has two moving violations on his license was followed by a police car. When the policeman put on his vehicle's red flashing light, the Canfield driver panicked, leaped from his vehicle, ran back to the policeman and professed his innocence.

"Calm down. I'm not going to give you a ticket," said the policeman, according to Canfield. "My wife told me not to come home tonight unless I bring her some Canfield Diet Chocolate Fudge Soda. Where can I get it?"

Chocolate-craving dieters experiencing that problem were unconcerned about the cost. They mailed blank, signed checks to the firm pleading for a six-pack (which retails for $1.99). Their checks were returned.

One man walked up to Greene on the street and asked, "Can you tell me where to get some Canfield's?" He replied, "The soda pop?" The man answered, "No. The stock."

Every day since the column appeared in January, Greene has fielded such inquiries. Just a few days ago, at a funeral in Ohio, people came up to him to ask about the firm.

Because Greene's column provided coast-to-coast exposure and an insatiable demand for the product, Canfield's, unable to produce enough, has franchised its line of nine flavors of diet sodas to bottlers and distributors across the country, among them Joyce Beverage. The firm makes the extract, then ships it to the bottler, thereby eliminating hefty freight charges.

While Alan Canfield and Bob Greene have endured dozens of interviews, the man Canfield calls "the genius" who created the product, its chief chemist, Manny Wesber, shuns the limelight.

Canfield says that while Wesber was cashing a company paycheck earlier this year, he was asked if he worked for the firm that made the diet chocolate fudge soda. When he revealed that he had invented it, the clerk started screaming, "He invented the soda pop. Here he is. Over here." Tellers and customers surrounded him, staring.

It took Wesber approximately 18 months to create the diet chocolate fudge soda, which he calls "his baby." Wesber started working on the formula in 1971, when Canfield brought him a pound of chocolate fudge. "I told him," says Canfield, "that if he could make a diet chocolate soda that tasted this good and had no calories, we wouldn't have to work so hard."

Periodically, while Wesber labored at combining chemicals to precisely duplicate the taste of chocolate fudge without using any chocolate, Canfield replenished the supply of candy. About 40 different ingredients go into making up the artificial chocolate, the aroma, the flavor, the base.

The result is a beverage that smells and tastes like chocolate. It is a top-secret formula he believes competitors will have trouble duplicating. "We don't keep the money in the safe now," Canfield says, then laughs. "We've got the recipe (there)."

Not everyone likes the recipe. Comments have ranged from "fantastic" to "terrible." While some people have gagged after just a swallow, proclaiming the aspartame-sweetened drink too rich, too chocolaty, or too sweet, others drink it throughout the day.

In addition to taking small swigs to banish chocolate cravings, Bob Greene has found a new use for the product. He recently put some vanilla ice cream in a glass, poured the diet chocolate fudge soda over it and reveled because the combination tasted "just like a chocolate soda at the soda fountain."