A plague of desert locusts of biblical ferocity is sweeping across the Horn of Africa. At least 67 separate swarms, with 4 billion locusts to a swarm, have been identified in Ethiopia and Somalia this summer.

In the United States the locust's smaller cousin, the grasshopper, is eating its way in near record numbers through the grass, corn and bean fields in the Dakotas, Nebraska, Kansas and Missouri. In the rich alfalfa fields of eastern Calorado, farmers have counted 150 grasshoppers per square yard.

"The last year it was this bad was 1958," said Richard Cowden of the U.S. Animal and Plant Health Service. "There are crop growers in Colorado who are already devastated this year by grasshoppers."

Not since the Dust Bowl days of the 1930s has the United States been so assaulted by pests. The gypsy moth in the Northeast, the fire ant in the Southeast, the corn borer in the Midwest and the grasshopper in the Plains states now infest the nation in record numbers.

And the picture is the same through much of the rest of the world. Insect pests, long under control, are making a comeback.

Mosquitoes are one of the best examples, biting the world's population in such numbers that malaria is a worldwide disease again.

"Malaria is rapidly becoming a major disease in parts of the world that haven't been troubled by malaria in 20 years," said Dr. Clifford Pease of the U.S. Agency for International Development. "Malaria is on its way to becoming a major international problem."

Rising counts of malaria are recorded in Thailand, India, Lebanon, Brazil, Guatemala, Honduras, Columbia and Haiti. Fully half of the 200 million cases of malaria that struck the world in the last year have stricken Africa. An estimated 1 million children died from malaria in the last year.

The reasons for the rise in pestilence around the world are not simple. They involve climatic variations, changes in agricultural patterns, the banning of certain pesticides for environmental reasons and widespread insect resistance that makes others ineffective.

The main reason for the increase in malaria, which the World Health Organization estimates has risen more than 25 percent in the last two years, is the rapid advance of mosquito resistance to insecticides.

No fewer than 43 species of malaria-carrying mosquitoes are immune to the potent BHC (benzene hexachloride) and Dieldrin, which almost wiped out the malaria mosquito 20 years ago. And the disease has grown resistance to antimalaria drugs.

Whatever the reasons, the results are devastating. India was able to reduce the number of its malaria victims from 100 millions in 1952 to 60,000 10 years later. By 1976, the number was back up to 6 million. WHO officials say the number are still on the rise. Neighboring Pakistan and Bangladesh are suffering similarly.

The reasons for the locusts in the Horn of Africa are even more complex. The drought that plagued the region for more than five years gave way a year ago to unusually heavy rains, which weather forecasters say will persist for at least another year.

The rain did two things. It gave the locusts the moist soils they need to breed, and it grew the vegetation they need to thrive. So quickly did the locust population grow that as many as 80 swarms were counted early this year.

One swarm flew across the Indian Ocean to Pakistan and India, where the locusts were brought under control through extraordinary effort. Most of the locusts now are in Ethiopia and Somalia, but there are some in Yemen, Aden and Oman across the southern end of the Arabian Peninsula.

Most pesticides are useless against the adult locusts, which grow to a length of four inches and come together in swarms that block out the sun for hours at a time when they take to the sky.

Each locusts eats its weight equivalent every day. They eat seeds, leaves, flowers, fruit and bark. When they swarm on to trees their weight alone breaks the limbs, this year the 50 swarms identified in Ethopia and the 17 in Somalia have eaten huge swaths of grassland as well as grains like millet, teff, sorghum and corn.

"The people in Ethiopia and Somalia claim the locusts haven't damaged the food crops yet," said the U.S.Department of Agriculture's Joseph Gentry, a leading expert on the desert locust. "If that's true, It's only a matter of time before it happens."

It was a similar cycle of drought followed by wet weather that brought out the grasshoppers in the American West. Like locusts, grasshoppers will eat almost anything. They'll feed on range grass, but prefers crops if they can get them.

"I've seen them defoliate oak trees, and that's pretty hard eating," said Homer Autry of the U.S. Animal and Plant Health Service. "We have pictures of them eating wooden fence posts and pitchforl handles. Anything with cellulose that will keep them alive."

What Autry says is the worst grasshopper infestation in 20 years may have been triggered by more than the right weather conditions. The nationwide ban on the persistent pesticides like heptachlor, Dieldrin, Aldrin and Chlordane may also have something to do with it. The allowable substitutes like malathion are more expensive and less effective.

Making matters worse is the trend among farmers to make their croplands bigger and bigger, thus removing any effective barriers to grasshoppers migration. The grasshoppers can literally eat their way across the country.

"It's an ideal situation for pests to build up devastating epidemics," the Animal and Plant Health Service's Autry said. "If you have a one-acre field, there's just so many bugs can build up in that field, but if you have thousands of acres far as the eye can see you're going to get millions and millions of bugs."

Grasshoppers don't migrate as widely and as quickly as locusts, but they move a lot faster than most other insects. The grasshopper has already moved into Texas, where 200,000 acres of rangeland received a treatment of malathion paid for by the federal government. It was one of the few places the United States sprayed with pesticide this year to stem the grasshopper tide.

Why? Because after World War II, the farmers and governors of the 15 western states where the grasshopper was perennial trouble agreed with the federal government that the persistent pesticides worked so well on cropland that federal intervention was no longer needed.

The federal government still sprays some grassland, because so much of it is federally owned, but even here the United States bears only one third of the cost. And it will only pay for registered insecticides like parathion and malathion, whose persistence is more than a few days.

"We lost the chemicals that knock the population way down," Autry said. "And unless you can kill off more than 90 percent of the pest population, they're breeding faster than you can kill them."

Autry and Cowden claim that the loss of persistence pesticides hurts even more in the war against other pests like the gypsy moth, the fire ant and the corn borer. Even together, these three pests are less spectacular then the grasshopper, but they now cause at least as much economic damage.

"I've recommended to all the environmentalists," Autry said the other day, "that they go and sit down on a fire ant mound for 10 seconds, and I guarantee they'll see the light a day on Mirex (mostly banned by the Environmental Protection Agency) for fire ants."

The situation is analogous in the war against the African desert locust. Ten years ago, the Departmeny of Agriculture financed the spraying of the African Horn with persistent pesticides that all but wiped out a threatening locusts epidemic. This year, no such spraying was permissible.