Like the biblical plague, or the onslaught that cost farmers upwards of $60 million in the late 1950s, millions of grasshoppers are moving through the rangelands and crop fields of the American Plains.

In Kansas and Nebraska, farmers are demanding that the federal government allow them to use Aldrin and Dieldrin, pesticides currently banned.

In southeastern Colorado, the grasshopper count has reached 55 per square yard. Eight to 10 per square yard - a number sufficient to eat as much grass per day as a cow and a calf - is considered a serious infestation by the Agriculture Department.

More than 160,000 acres in Wyoming are being sprayed with pesticides, and it is not a particularly bad year there - yet.

But it is a bad year in Colorado. The legislature will meet in special session tomorrow to consider setting up a $7.2 million emergency aerial spraying program on 1.3 million acres in 19 eastern counties.

Gov. Richard D. Lamm warned Friday that the spraying has to be done quickly because a single grasshopper lays 300 eggs and another grasshopper hatch is due to begin Thursday. He made his comments after returning from counties where the insects danced on his shoulders and hair. Without spraying, damage to rangelands along could exceed $4.5 million, the state Department of Agriculture said.

Describing the scene of the infestation. Colorado Agriculture Commissioner J. Ewin Goulding said, "It's simply a swarm. You look at an alfalfa field and don't see much until you go out in it. Then it literally comes alive."

There is no overall estimate of the damage caused by grasshoppers this year. But Lamm said, "we know it will be vast."

The grasshoppers pose a threat to pastures and crops such as irrigated corn, alfalfa, sugar bets and soybeans, entomoligists said, but not to the tougher wheat crop, much of which has been harvested.

State Agriculture Department officials said they planned to use the pesticide Malathion on the rangeland and Sevin on the crops.

When Lamm toured the region earlier this week, a county extension agent in Cheyenne Wells reported that grasshoppers had eaten paint off buildings, had destroyed vegetable gardens and were munching away in irrigated corn fields.

The end of the long Western drought probably triggered the grasshopper assault, agriculture experts said. It happened in the 1930s and in the late 1950s when drought followed by rain produced major grasshopper outbreaks that helped make dust bowls out of rangeland and farms.

The most recent drought destroyed grasshopper predators. The rains that arrived on the plains late last year were just in time to support grasshopper hatching. "Last winter was perfect in terms of environmental conditions for grasshoppers," said Goulding.

The outbreaks have not been limited to the plains. Hordes of grasshoppers are chopping their way through fields of alfalfa in southeast Lower Michigan and swarming over the Arizona cities of Phoenix, Tueson and Tempe.

But the most severe infestations are in the counties along the border separating Kansas and Nebraska from Colorado.