William P. Lear designed and developed the Lear Jet, perhaps the most successful executive airplane in the world. He also invented the automatic pilot for jets.

For people who drive rather than fly, Bill Lear invented the car radio. Years later, he invented the eighttrack stereo for cars. He held more than 150 patents.

In the late 1960s, he put $17 million of his own money into the development of a steam-powered automobile, because, he said, "I wanted to develop something that would prove that I wasn't just lucky."

Prove it to whom?

"To the world," he said.

The car never went anywhere. But when he died of leukemia in a Reno, Nev., hospital yesterday at the age of 75, Lear was on the verge of producing a new executive plane, the Lear-fan, which is covered with molded platic held together with glue.

Lear claimed that his new plane was the safest aircraft ever designed. It is powered by two gas turbine engines that turn a single four-bladed propellor in the rear. He said it would also prove to be one of the most economical planes ever to fly - a cruising speed of 400 m.p.h. at a rate of 12 miles to the gallon, or only 25 per cent of the fuel consumption of the Lear Jet.

"I'm not a tinkerer," Lear said recently. "In fact, I'm not very good with tools. My outstanding ability is to recognize a market and to fill it."

This ability made Lear a millionaire many times over.

He began with almost nothing. William Powell Lear was born in Hannibal, Mo. His father was a carpenter and Lear once said that "my father worked his . . . off to earn a decent living. I never saw anyone work so hard. He hauled oil riggins, never had proper equipment to do the job."

When Lear was 6, his parents separated and his mother took him to Chicago. He finished his formal schooling with the eighth grade. At 14 he became a mechanic and at 16 he joined the Navy and studied radio.

"I remember working out a blueprint for my future when I was 12 years old." Lear told and interviewer for The Saturday Evening Post in 1986. "I resolved first to make enough money so I'd never be stopped from finishing anything; second, that to accumulate money in a hurry - and I was in a hurry - I'd have to invent something that people wanted; and third, that if I ever was going to stand on my own feet, I'd have to leave home."

After his World War I naval service, Lear learned to fly and worked as a radio engineer. One of his first inventions was a nonbattery home radio receiver, but it was not until 1924 that he had his first major suceess. He invented at radio that would fit into an automobile.

"That was so people wouldn't have to rush home and listen to 'Amos 'n' Andy,'" he said last month.

Unable to get financial backing to produce it himself, he sold the device to Montorola.

In the next several years he founded a number of companies of his own and several of them failed. He also married three times and was divorced three time. In 1934, he designed a radio frequency amplifier that could be used in any radio set. The Radio Corporation of America bought it from him for a substantial sum and Lear used to found Lear Avia Corp. in Dayton, Ohio.

By 1939, more than half of the private planes in the United States were using radio equipment and direction finders made by Lear Avia. In that year. Lear founded Lear Inc. During World War II, the company did about $100 million in government business.

In the post-war years, Lear invented an automatic pilot that could be used in jet aircraft. Between 1950 and 1962, sales of Lear Inc. doubled to $90 million. It was in these years that Lear decided to go into the executive jet aircraft business. When the directors of his company refused to authorize the huge sums necessary to develop and produce what became the Lear Jet, Lear sold out his interest and started again on his own.