Extraordinary veggies produced by ordinary plant breeding

In perhaps as little as a decade, and certainly by the turn of the century, a new generation of super crops should begin to sprout on farms and in gardens around the world. The advance of genetic engineering - the ability to splice favorable genes from one plant onto another - is expected to see to that.

Conceivably, the drought tolerance of a desert grass could be fused into water-loving corn to turn it into a crop for arid regions as well. Tomatoes may be made to withstand frost, and garlic - its flavor intact - may no longer linger on the breath.

The possibilities appear almost limitless. But all this remains a few years down the road.

Meanwhile, plant breeders continue to improve crops through selection and cross-breeding, as they have all century long. The improvements might not appear as dramatic as those promised by gene splicing, but over the years they mount up. Sometimes straightforward cross-breeding produces a new variety worthy of the term ''super crop.'' Sugar Snap, winner of an All America Selections gold award a few years ago, was one such variety.

Until Sugar Snap came along, few people dreamed that a fully mature garden pea could be eaten, pod and all. Sugar Snap is a tall climber, getting well above 6 feet in my garden. That is its drawback, in the view of some people, and shorter varieties soon followed.

Now among the list of introductions for 1984 comes Sugar Ann, the latest of these short varieties and considered by many to be the best of them all. Sugar Ann produces pods that are as plump and sweet as its lofty parent, but on vines that are a mere 15 to 18 inches tall. Incredibly, it produces as large a crop as Sugar Snap and matures two weeks earlier.

Plant the two of them in your garden for an extended harvest of sweet peas. Just as your Sugar Anns go past their peak, the Sugar Snaps will come into their own. An All America Selections (AAS) award winner, like its illustrious predecessor, Sugar Ann is carried by most seed houses.

The new releases for 1984 are far too numerous for all of them to be listed in this space. Among those worthy of mention is another AAS winner, the Celebrity tomato.

Celebrity outperformed all its rivals at test gardens around the country, yielding well in the blistering heat of summer, when many varieties set fruit poorly. It starts producing 8-ounce fruit 70 days afer setting out on medium-sized vines and is described as ''full of flavor'' by trial growers.

Butter Bush is another impressive newcomer to the tomato field. This Geo. W. Park Seed Company exclusive brings tall-vine flavor and productivity to a determinate vine. The 31/2-foot vines produce fruit until frost. Among processing tomatoes, Johnny's Selected Seeds offers a Canadian-bred variety, Belstar, which produces fruit almost twice the size of the long-recognized Roma variety.

Another processing variety, by Stokes Seeds, is Heinz 1765, which produces large globe-shaped fruit that mature in 73 days.

Stokes is also introducing a butter-yellow sweet pepper, Butter Bell. The bell-shaped, thick-walled fruit begin maturing in 70 days. Another good new pepper is Joseph Harris Company's Key Largo, a heavy producer of 6-inch-long peppers that turn from pale green, through yellow, and finally to red. Guerney Seed Company is introducing Pick-Me-Quick, a pepper developed by South Dakota State University to withstand both the cold springs and hot summers of the Midwest.

Tam is a new variety of Jalapeno pepper with much of the zing, but none of the bitterness, associated with the old kind. Henry Field, Earl May, and Twilley seed companies are listing it.

Carrot growers will be interested in Orlando Gold offered by the Field, Guerney, and Stokes companies. The new carrot contains 50 percent more carotene than any other variety.

The Vermont Bean Seed Company may have started out with beans, but it has long since branched out into other lines. This year it has come out with a trio of lettuces that withstand summer heat. They are a globe-headed variety, Ballade , and two loose-leaf types, Green Wave and Red Fire (named for its intense red color).

The W. Atlee Burpee Seed Company has introduced two new cucumbers, improved varieties of old favorites. They are Burpee Hybrid II and Burpeeana Hybrid II. Both are gynoecious (all female) and more productive than their predecessors.

Burpee has also introduced Limelight, a new honeydew melon that slips from the vine the moment it reaches peak flavor.