It was nothing hush-hush, nothing ultrasensitive, but some of the best brains in the country, the boys on Project S-131 got together in Atlanta last week to resume pondering a mystery of the chicken and the egg.

There will be no cackling, please.

The age-old chicken and egg riddle has a fascinating side of enormous economic consequence -- how to make a tougher eggshell -- and that is what S-131 is all about.

In selected universities around the country, researchers using money from the U.S. Department of Agriculture (hence the Project S-131 label) are trying to find ways to improve eggshell quality.

It is not chicken feed in a multibillion-dollar broiler and egg industry. By some estimates, roughly 7 percent of the nation's eggs cannot be used because the shells are inadequately formed or are too fragile.

"The No. 1 problem in the industry is cracked eggshells," said Dr. George Mountney, a USDA egg expert, "and it has increased because of the growing amount of automation. . . . The hen doesn't always lay a perfect egg, and that's what these researchers are studying."

You can begin to get an idea of the size of the problem from the figure that reflects the eggs that were usable.

Last year, according to USDA, America's hens laid 69.5 billion eggs destined for grocery shelves, food processing and export; 4.2 billion eggs were hatched into chicks for eating, and 476.6 million were hatched into layer chicks for the egg-production line.

Now, most of this high-volume egg-laying is occurring in highly mechanized, assembly-line-type chicken coops where the gentle human touch is missing. The mechanical gathering, washing and packing procedures all take their toll on fragile shells.

Enter now men like Dr. David Roland of Auburn University, who is regarded as one of the country's leading figures in eggshell quality research. Ronald's idea is that if you can improve the shell -- even slightly -- before it leaves Mother Hen, then you are talking turkey, as it were.

Roland's studies indicate that poor shell quality means that for every 100 eggs collected, 7.7 more eggs don't reach collection points because of weak shells or no shell. That's more than 5 billion unusable eggs per year.

Working a little basic math from that, Roland figures that eggs that would have sold for $356.7 million in 1980 were lost. They had yolks and whites, but their shells were not firm enough to allow their use.

Mountney coordinates the work of Roland at Auburn and other universities (leaders include Florida, Georgia and Penn State) in the S-131 project on shell quality.

Now, laboratory work on shell quality might not seem quite as dramatic as finding a cure for cancer or the common cold, but Roland won't buy that. He brings missionary zeal to the quest for a tougher eggshell.

"If I could improve shell quality by just 1 percent, it would mean a lot of money to the country," Roland said the other day. "A lot of people don't realize how much research can help.

"If I could make an improvement in shell quality and this would increase the food supply of the world, it would give me a sense of satisfaction. . . . I know quality can be improved. I'm an optimist."

Research into feeding, timing and housing factors have created a sort of revolution in egg production since 1950. Back then, a hen with a typical laying life of 14 months was cranking out about 120 eggs per year. Now, she produces about 260 per year.

Much of this increase is due to an improved mix of nutrients in the hens' diets, as well as the discovery that a controlled environment -- warmth, more light -- would stimulate the chicken. "From the cackles, you can tell when a bird is happy," Roland said.

Other experts regard Roland, 38, a Georgia native, with a certain awe. Poultrymen in New Zealand and the Far East have called Roland to their sides for advice. Dr. Thomas J. Sexton, head of USDA's Avian Physiology Laboratory at Beltsville, Md., describes Roland as "a novel thinker."

One of those novel thoughts, resulting from his work as Auburn, has just been published. Roland found that by changing the time of feeding from morning to evening, when shell calcification begins inside the chicken, a better shell would result.

"It occurred to me that if the feed goes in when the hen is calcifying, the nutrients would go right to the blood. It proved out," Roland said. Ideas of that sort, Mountney and Sexton indicated, soon work themselves into practice.

Roland's studies also disproved a long-held belief that shell quality diminishes as a hen grows older. Shell quality remains the same; the egg becomes larger, he found, which causes more shell breaks or inadequate shell formation.

So, the challenge is still there: how to toughen that shell. What Roland and his research brothers are after, really, is one of the mysteries of life.

"Looking for the Fountain of Youth, in a manner of speaking," as Roland put it.