There's no question that the world of biology is undergoing a revolution of far-reaching implications. Scientists can transfer genes from one organism to another, can program genes to produce desired traits, can "custom-make" new kinds of plant life.

But if you think the first fruits (and vegetables) of this revolution will be something for the 21st century, ponder again. Already some of the benefits of the new research are making an impact.Through its Agriculture Research Service, the U.S. Department of Agriculture sponsors ongoing research into ways of improving our food supply using both traditional and innovative biotechnological methods.

Here's an update on some of the latest findings from research stations around the country. It might be a little while before some of these new foods show up in stores and on your table, but there are certainly developments to watch.

ONE FRESH TOMATO

The search for a more perfect tomato is almost as involved as the search for a better mousetrap. The latest quest: a tomato that stays fresh longer.

Researchers have discovered that a sugar in tomatoes stimulates ripening. If the sugar's effect on tomatoes can be genetically programmed to slow the ripening process, it could help prevent spoilage at a savings of $5 billion a year, says the USDA.

In other tomato news, scientists advise that for best tomato flavor, cut it as close to eating as possible.

When a vine-ripened tomato is cut, it releases natural chemicals that give it a pleasing aroma and fresh taste. About three minutes after you slice into the fruit, the aroma starts to fade away. That's why the tomato you put in your sandwich when you're packing your lunch in the morning has little fresh tomato flavor left by noon, says USDA researcher Ronald G. Buttery. "Wait until the last minute to slice a tomato."

He's also found that mom's advice about not putting tomatoes in the refrigerator is good advice. "Tomatoes kept refrigerated for seven days had less of the aroma-imparting flavor chemical than did tomatoes kept at room temperature."

PURE WHITE POTATO

A new baking potato is on its way to some grocery shelves this fall. The Coastal Russet potato was recently released by Agricultural Research Service and experiment stations in New York, Florida, Virginia, New Jersey and Maine.

The potato was developed specifically for growing conditions along the East Coast, but researchers have found that it can be grown throughout the United States. It may take a little longer to show up in stores out West, but it's on its way.

The potato is whiter and more moist than Russet Burbank, the most common baking potato. Most potatoes turn light beige inside when baked, but not Costal Russet.

Not only is the potato pleasing to the consumer, but it is also resistant to three of the most common potato diseases, so growers like it as well. The potatoes are uniform in size and as many as 90 percent are marketable. Not only that, but it takes 30 to 40 days less time to mature than the Russet Burbank.

SWEET POTATO FRIES

Speaking of potatoes, are American consumers ready for sweet potato French fries? A USDA scientist thinks so. William M. Walter Jr. thinks that French frying the sweet potato may liberate it from its traditional place at the holiday dinner table and put it on restaurant menus next to the more popular white potato.

A Washington, D.C., restaurant that has begun selling the fries uses 100 to 150 pounds of sweet potato French fries each week.

Walter says sweet potato fries offer good flavor as well as good nutrition. "After carrots, it's one of the best sources of beta carotene, which the body uses to make vitamin A."

The sweet potato is one of the leading vegetable crops worldwide but has been under-utilized in the United States, says Walter. In 1987, the United States produced 38.6 billion pounds of white potatoes, compared to 1.2 billion pounds of sweet potatoes.

Walter hopes the idea of sweet potato fries will catch on and change that. Tests have also shown, he says, that storage stability shouldn't be a problem if industry wants to adopt sweet potato French fries. After a year of frozen storage, the cooked fries retained their flavor, texture, appearance and beta carotene.

SWEET ON MINI-MELONS

You don't have to rearrange the refrigerator to find a spot for Mickylee or Minilee. These two new miniature watermelons should become big sellers here and abroad, according to a USDA marketing specialist.

Firmer, crisper and sweeter than other watermelons big and small, the size and flavor of these 5- to 12-pound melons gives them marketing advantages over their huge 20- to 25-pound cousins, says Lawrence A. Risse.

Big watermelons have fallen victim to demographic changes in the U.S. in recent years, where per capita watermelon consumption has dropped about 30 percent in recent decades - from 17.9 pounds per year for 1951-60 to 12.8 pounds for 1971-80.

Compared with big melons, the new varieties have much smaller seeds and fewer seeds per volume as well.

The mini-melons also show promise as an export product, says Risse. The USDA test-shipped the melons to Rotterdam and London where they were well received by importers. The melons held up well during their two-week trip even without refrigeration.

The new varieties grow anywhere other watermelons are grown, and they can be grown out of season - planted in August or so for fall harvest; big melons planted late don't do as well.

HOUSEPLANT ASPARAGUS

Keep houseplants out of reach of pets and children, safety experts advise. But here's one you won't have to worry about. Not only that, you can even cook it for dinner.

USDA scientists have come up with a new asparagus that can do double duty in a hanging basket and on the dinner table.

Not that you'll get enough stalks from one hanging basket to feed a family, says plant geneticist Gilbert D. McCollum, "but you can certainly get a few for your salad. And it is a pretty plant."

He began cross breeding garden variety asparagus several years ago in hopes of finding a way to add resistance to crown rot disease to garden asparagus.

Crown rot is one of the reasons that asparagus remains an expensive vegetable. Each year, the disease costs commercial growers about $100 million.

As yet, crown rot resistance is still elusive, but in the meantime, McCollum came up with the houseplant variety.

The asparagus is a hardy plant that will grow continuously indoors, although it has a tendency to become pot bound, he says. "And it will survive the winter outdoors, although the foliage will die down and then come back in the spring.

MILK WITH A LITTLE FIZZ

A lot has happened to milk over the course of history. It has been bottled, pasteurized, homogenized, fortified with vitamin D, skimmed of its fat, powdered, flavored and put in plastic containers.

Now scientists want to add something more - a little fizz.

USDA researchers in New Orleans are looking for new ways to use surplus powdered milk and have developed what could be called soda milk.

Actually there are two types of this carbonated brew - one with artificial strawberry flavoring and the other mixed with filtered apricot juice.

Soda milk is made by bubbling carbon dioxide gas through a mixture of water, powdered nonfat dry milk, flavoring or apricot juice and other ingredients. The mixture is kept under pressure and bottled right away so the carbonation doesn't escape.

You get that tingling, refreshing sensation of carbonation that you get in soft drinks, and you're also getting calcium, protein and vitamin C.

In tests, the strawberry-flavored milk stayed fresh up to six months under refrigeration; the juice mixture lasted two to three months.

"We've shown that you can make a carbonated drink in which the powdered milk stays suspended and doesn't separate in the mixture," says researcher Ranjit Kadan. "Commercial companies would have to refine the process and add other flavors before you'll find it in the supermarket."

But he hopes the carbonated milk beverages would spur consumption of milk. Between 1975 and 1985, per capita consumption of milk in the United States dropped 12 percent. During that same time, per capita consumption of soft drinks increased 68 percent.