There probably will be more vegetable gardeners in the U.S. this year than ever before. Many new ones will try their luck in hope of reducing the cost of food. Their success will depend to a large extent on ability to control insects, diseases and weeds.

There are ways to control most insects, diseases and weeds without risk to your health and with a minimum of trouble.

Insecticides kill insects because they affect a life process like respiration, digestion, circulation and nerve reactions. A person also might experience some effect if enough of the chemical gets into the body.

Anyone who plans to use an insecticide should first read the entire label on the container, the directions for its use and the warnings. The main precautions are to avoid getting the inseticide into the eyes or mouth or on the skin.

Many gardeners assume that if an insecticide or fungicide (for plant diseases) is effective against one kind of insect or disease, it should be effective against all. That is not true. It is effective only against those listed on the label.

In fact, with only a few exceptions, use of fungicides by many gardeners is a waste of time and money. The fungicide will not cure; in most cases it can only prevent infection and must be applied before infection occurs. Most gardeners cannot identify most diseases and don't know what treatment to use. There are books that descrube the effects of many diseases of plants, but they are incomprehensible to most gardeners.

The best protection against disease in the vegetable garden is to buy disease-resistant varieties of plants.

Three of the most serious insect pests in most vegetable gardens are aphids (plant lice), spider mites and Mexican bean beetles.

There is scarcely a food plant that some kind of aphid does not attack, damage, stunt or infect with a disease if it gets a chance. They innoculate vegetable plants with virus diseases through the saliva they inject into the leaf as they prepare to feed.

Research has shown that an aluminum foil mulch can repel aphids. Strips of aluminum foil more than double the yield of vegetables in experimental garden plots at the Beltsville Agricultural Research Center. They provide an effective barrier by reflecting ultraviolet rays from the sky. (Insecticides do not kill disease-bearing aphids quickly enough to prevent infection.)

Best results were obtained when 50 percent of the ground area was covered. Promising results also have been obtained with aluminum foil against thrips and other insects on rose bushes, dahlias, gladiolus, tomatoes, cucumbers and snap beans.

The foil also serves as a water-conserving mulch.

Many kinds of insects, including aphislions, wasps, yellow jackets, spiders and lady beetles, feed on aphids and other kinds of insects.

When an insecticide is used to control insects, invariably the beneficial insects are destroyed.

The use of soap sprays of insect cntrol was demonstrated as early as 1842. As the more effective synthetic organic insecticides were developed, use of soap was largely discontinued.

Solutions derived from bar soaps performed well but were not as easy to use as liquid soaps and detergents. Of the liquids, Ivory Liquid dishwashing detergent proved the most consistent control, especially when used at 1 to 2 percent.

It is believed these sprays are less damaging to beneficial insects than are most synthetic organic insecticides.

Most sucking insects feed on the undersides of the leaves, which should be sprayed also.

A measure of control of aphids and mites can be achieved by using the hose on them at full pressure.

The best way to control Mexican bean beetles is to pick them off and squash them.

A recent book, "Rodale's Color Handbook of Garden Insects," by Anna Carr, published by Rodale Press, Emmaus, Pa., with 300 color photographs of garden insects in the egg, larval pupal, and adult stages, will enable you to identify almost any insect found in the vegetable garden or orchard.

The best way to control weeds in the garden is to pull them up while they are small, and also to use a mulch. An herbicide (weed-killing chemical) used in the garden is likely to do more harm than good.

The National Capital Area Federation of Garden Clubs will hold a "Horticultural School" at the Auditorium of the National Arboretum, April 8, 9 and 10, on pest control. The fee for the full course is $10 for members, $12 for nonmembers, and $5 for only one day. For more information and to register, contact Mrs. Harry Dresser, 12853 Hunstman Way, Potomac, Md. 20984, 762-6647.