. . . It makes you tingle when you're single, It makes you trouble if you're double. . . . -- From "Gen Sing," popular song.

Puckish Dr. James A, self-styled "chief quack" among U.S. Department of Argiculture scients, knows some secrets that 1 billion Chinese may be lusting after.

He knows all about ginseng. Knows where to find it growing wild in the shadow of the Capital Beltway. Raises it at home.Believes, like the Chinese, that ginseng does wondrous things for the mind, if not the body.

Ginseng, a plant that is thought to increase human stamina and endurance, not to mention sexual function, figures in the new air of scientific cooperation between the United States and the People's Republic of China.

The chinese want to know all there is to know about American ginseng, which is in big demand in the Orient. By USDA estimates, some 644,000 pounds of the root were exported last year, producing about $39 million in income.

In agricultural terms, this is not small potatoes. The best grades of wild ginseng, found extensively in the Appalachian hardwood forests, fetch as much as $170 a pound. The best commercial grades, from farms in Wisconsin, Ohio, Kentucky and North Carolina in the main bring considerably less but still are high-profit. Income of $10,000 from a half-acre plot is not uncommon.

Demand is such for the wild variety that it is protected by an international endangered-species treaty and its harvest in the United States is closely regulated by the Interior Department and state governments.

At the prices it commands, any buyer would want to grow his own. So a team of five Chinese scientists has been here this month, spending time with Duke at the USDA Research Center in Beltsville and visting farms around the United States to get more ideas about production techniques.

"They want more ginsent, but they would rather grow it themselves," said Duke. "We think they may eventually buy some American ginseng germ plasm, but I feel the wild root, which is more potent than commercial ginseng, still will be in great demand."

Duke's specialty at Beltsville is the study of medicinal plants, but ginseng is the biggest attention-grabber. For centuries, the folklores of both East and West have attributed the ginseng powers of renewal. Makes an old man young, in the words of a song Duke's bluegrass band plays.

According to Duke, studies in the Orient have found hormonal substances in ginseng that tend to substantiate the idea that it is an endurance-builder, when taken regularly in the form of tea or powder or as a food additive.

Well, the widsom of the East eventually finds its way here, and sure enough, the ginseng lengend has reached us at hormonal sure force. "Growing Ginseng" has become one of the most popular of USDA's farmer bulletins. Ginseng products abound in health-food stores.

Among the places the Chinese scientists visited was such a store in College Park, where, according to manager John Dennison, they were suprised at the variety of ginseng products: a soft drink, tea, teabags, cigarettes, roots and powder, extracts, granules, tablets, capsules.

"People are becoming quite sophisticated about ginseng," Dennison said. "They are able to distinguish between the different grades. . . . The aphrodisiac is part of the folklore, a commercially popular idea, but it is not advertised that way the China or Korea and we don't play up that aspect."

When Jim Duke took his Chinese friends to a secret patch of wild ginseng growing not far from the beltway, he said, "They rooted around in it like a bunch of babies."

For his own part, scientist Duke is doing a private study of 300 plants he put in the woods behind his home a couple of years ago. "FOR MY OLD AGE," HE SAID. "i sit in the shade and watch it grow, dreaming my Oriental fantasies."