From on high, toward horizons that reach to the edge of the world, this land is a quilt of mellow gold and lush green.

The gold is the tassel of the great cornfields; the green is the soybean that hunkers close to the coal-black soil, some of the richest soil anywhere in the world. At ground level, the air is sweet with the smell of ripening corn.

But the riches are illusory, in a way.

There has been no rain for two weeks and the temperatures have ranged into the middle and upper 90s, threatening the huge Illinois granary with the same devastation the heat wave has brought to other parts of the Midwest and Southwest.

Agricultural experts say the heat in Illinois already has been bad enough to cut corn and bean yields by as much as 10 percent. Without significant rain in the next week or so, the damage will be enormous.

The effect on prices is staggering. A brief shower here Friday sent soybean prices down 40 cents a bushel and corn down 10 cents in a few minutes at the Chicago Board of Trade. Prices moved back up as the rain stopped.

In fact, in a year that already looks bleak for farmers -- the Agriculture Department is predicting an income drop of 20 to 40 percent for farmers because of sharply rising costs and low farm prices -- the drought offers a small measure of hope. As production declines, prices may rise.

A USDA forecast earlier this month estimated a 6 percent decline in corn production, partly because of dry weather. And even as the figures were being released, the department's top economist was saying the latest report on the weather indicated an even higher toll on the crop.

It is enough to make farmers like Darrel E. Glenn, who watches over 670 acres outside this tiny McLean County town, go stark raving mad. A good steady rain, or lack of it, can make the difference between boom and bust. g

But Glenn, 53, has been farming most of his life, which is long enough to know there is a rhythm to these things. Sooner or later, there will be rain; sooner or later, temperatures will fall.

"The next 10 days will be critical for our corn and soybeans," he said. "As of July 4, we had a real decent-looking crop . . . then came the heat and no rain. You feel real good, but you realize you're at the mercy of the good Lord. It kind of brings you to your knees to realize someone else has some say-so over it."

As the stockbroker watches the ticker and the navigator the stars, Glenn watches the sky for guidance. Friday morning, it clouded and rained a bit, and his heart jumped. After a few minutes it stopped, and Glenn went back to watching the sky for signs of relief.

There is a certain irony here in McLean County. Nature has made this soil among the world's best and its farmers among the most industrious. It is so rich that a "bad" year still can mean McLean farmers will outproduce the rest of the state.

This county produced 48.8 million bushels of corn and 11 million bushels of soybeans last year -- more than any other Illinois county. McLean farmers averaged 143 bushels of corn per acre, spectacular when compared with the national average of 108.

"If we can average 108 statewide this year [it was 118 in 1979], we would consider this a good year," said Dan Zeicker, market adviser for the Illinois Agricultural Association, based in nearby Bloomington, the county seat.

"Corn is at the critical stage right now. We need rain in the next five to seven days, and if we don't get significant amounts, we will cut into the yield in a major way. But we don't yet have anything like they're seeing in Missouri and Arkansas."

Eugene L. Mosbacher, the county extension agent, agreed. "Naturally, good corn comes with above-average rain in July, and below-average temperatures. We've had no rain since July 5, and only five days of the month below 90 degrees."

Like others around Stanford, Glenn is more concerned right now about his corn than his soybeans. Corn, occupying about half of his 670 acres, is at the vital stage when it needs water and moderate heat for development of the ear. Soybeans won't reach their critical stage for a month or more.

"I don't know," Glenn said. "Last year, we had weather similar to this and I said the crop was hurt. Then wegot rain and we had a whale of a crop. You just keep hoping it will come."

Over at the Stanford Elevator Co., where the tall concrete silos can hold 1.2 million bushels of grain, manager Frank Rudisill agreed with Glenn, but reported that most farmers in the area believe this year's crop already has suffered damage.

The elevator, run on a cooperative basis by local farmers, is as up-to-date as most of the farmers in these parts. A television screen brings Rudisill the constantly changing price quotations from Chicago, about 100 miles to the north.

Glenn keeps on top of things by following radio reports about the market, checking in at the elevator (he is board chairman) and watching television at noon and at night.

Friday, he turned down the noontime television to talk to a visitor over a country lunch of steak, homegrown peas, salad and cole slaw. His wife, Evelyn, was excited over the 34 quarts of raspberries she had just put up for the winter. She was on her way to pick apples for several dozen pies she will bake and freeze for the cold months.

The conversation is not unlike those heard in most Illinois country kitchens. Farmers are still seething over President carter's embargo on grain sales to the Soviet Union and many, like Glenn, would like to see Agriculture Secretary Bob Bergland dry up and blow away. Carol Tucker Foreman, the assistant secretary, also gets bad marks from most farmers.

"If grain is going to be used as a weapon, they ought to move it over to the Defense Department," Glenn said, with a wry grin on his tanned face. "The embargo is the number one problem most farmers have with Jimmie Carter."

In a way, Glenn has a small conglomerate going, and like a good corporation executive, he keeps the figures close to the vest. "I'd have to go look at the books to see what this is worth," he said. His land, at $4,000 an acre, and his equipment are worth far more than $1 million.

Glenn's books are so extensive that a management specialist comes around twice a year to help him keep them in order and give him a computer analysis of how he's doing in relation to other farmers in the area.

He farms the land with the help of sons, David, 20 and Brad, 22, who just graduated from college with a degree in agricultural economics. Someday this small empire will be theirs, just as Glenn's parents got him started in the 1940s.

You could worry about the heat and the dryness, just as Glenn does, but you still would feel the same pull he has felt. It has to do with being your own man, although the seduction of hot apple pie and fresh raspberries figures into the equation.

"No, sir, no regrets," Glenn said. "It's a different life than it used to be, and we have some 16 to 18 hour days. But I'm doing fine."

Now, if only it would rain.