When new, 18 years ago, Donald Ranck's tractor cost him less than his Amish neighbor paid for seven handsome plow horses. Today, the Farmall is still chugging along on his Pennsylvania dairy farm, easily outworking the horses and giving Ranck time for other endeavors.

For more than a century, it has been that way increasingly on the American farm.

Typified by the reaper, the iron plow, the tractor and all their sundry improvements, machinery has revolutionized agriculture, increasing its productivity, making it the source of the nation's chief exports and transforming the American farm into a grainary for the world.

An irony in this success story is that the company that produced Ranck's tractor, the company that helped fire this mechanized revolution, the International Harvester Co., yesterday announced a massive reorganization in a struggle for solvency.

International Harvester is an end-product of the genius of Cyrus Hall McCormick, a Virginian who started the revolution 150 years ago with his invention of the reaper. From his toil came the giant Harvester firm, and from that came the Farmall tractor that dutifully serves Don Ranck. Until the 1960s, when it was overtaken by Deere & Co., Harvester was No. 1 in the world in farm machinery production.

But McCormick's legacy is not just the success of the reaper. He pioneered most of the business techniques that are commonplace in American business--advertising, warranties, field demonstrations, money-back guarantees, distributorships, franchising rights, fixed prices and time payments.

The Harvester story is worth remembering.

McCormick, as every schoolchild is told, created a simple horse-drawn device that cut grain--a job until then done by hand. More than any other invention, the reaper revolutionized farming and, as it pushed the world toward an ability to feed itself, it opened the way for the United States to become an industrial and mercantile power.

In its most primitive form, McCormick's reaper did the work of six men with scythes or 24 with sickles. In 1830, it took 37 hours to harvest an acre of wheat. By 1840, with reaper and thresher by then developed, it took just 11 1/2 hours. As additions and improvement were made, the reaper's record improved.

In the mid-1800s, the U.S. farmer produced food for himself and five or six people. Today, the farmer feeds 75 people, a feat made possible in part because of the high degree of mechanization and the larger farms it has helped spawn in rural America.

The form of the reaper has changed, of course--a self-propelled combine now cuts and threshes the wheat. But McCormick's basic invention is as important today as it was in 1831, when he perfected it on the family farm near Staunton, Va., about 150 miles southwest of Washington.

Eight years later, his family went bankrupt. Without money or credit, he went ahead and erected his first factory on the Virginia farm.

In the beginning, he almost had to beg farmers to give his reaper a trial. He advertised his first one for $50 in the Lexington (Va.) Union. No one bought it. In fact, he didn't sell one for nine years, even though it was patented in 1834 and even though it was clearly a labor-saver.

The patent expired in 1848, with McCormick then firmly ensconced in infant Chicago, operating the city's largest and busiest factory. Business boomed as Midwest prairies opened to farming. In 1848, McCormick built 800 reapers; a year later, he built twice as many.

But there were imitators and competitors and when McCormick attempted to extend his patent (the U.S. Patent Office turned him down), his corporate foes ganged up on him and set off one of the great legal and legislative battles of the century.

McCormick's competitors enlisted the likes of Lincoln, Stanton, Seward, Douglas and a raft of other big-name lawyers to fight his claim to exclusivity. Lincoln's first big fee, $1,000, is said to have come from the patent case.

The dispute dragged out for 15 years or more, and while McCormick lost in principle, he won for endurance and business acumen. He outproduced and outsold the competition, mainly because he was smarter.

In 1849, when able-bodied men rushed to the California gold fields, McCormick saw a natural opening. He advertised to warn farmers of a coming labor shortage and a big harvest. They girded for the storm by buying his reapers.

After the Homestead Act was passed in 1862, McCormick was right there with credit for new farmers. With free land and a Harvester on credit, a poor man could become an agricultural king without spending a dime. McCormick trusted them to pay (he always trusted farmers) and his faith was rewarded.

By the time McCormick died in 1884, his factory was producing 50,000 harvesting machines--more sophisticated versions of the early reaper--and U.S. farmers were growing wheat at a rate of 10 bushels for every citizen. When the Chicago factory opened in 1847, the rate was four bushels per capita.

In the 50 years after McCormick invented the reaper, his country had grown up. Chicago was the world's major wheat market and a rail, livestock and mercantile center, largely because of McCormick's invention. The flood of wheat money helped build the United States as a manufacturing nation; the economics of farming provided human muscle for the industrial machine.

The reaper, wrote an adoring McCormick biographer in 1909, "made all other progress possible by removing the fear of famine and the drudgery of farm labor."

Ranck, the Pennsylvania farmer, might not put it exactly that way, but that's what he meant when he compared Farm- alls and horses.