Visiting days at The Hockaday School in Dallas were a little embarrassing for Carol Spradley.

Most parents arrived at the exclusive girls' boarding academy in expensive cars. Spradley's father, a New Mexico rancher, always showed up in a red Ford pickup truck.

That was back in the late 1960s, Spradley recalled. Trucks weren't "in" then. And being "in" mattered, particularly to a teen-ager trying to make all of the right moves.

It's all different now. Pickup trucks, once the conveyance of Okies and rural bumpkins, have come up in the world. They are as likely to be seen in the parking lots of ritzy schools and country clubs as on the back 40.

"Today, it looks like everybody wants a truck," said Spradley, who works in Albuquerque for former senator Harrison Schmitt (R-N.M.), who drove a pickup around Washington during his Senate term.

Saying that "everybody" wants a truck may be overstating it a bit, but, plainly, the light truck has come of age as a flexible and popular form of transportation. The auto industry set a record for light-truck sales in 1985 -- 4.7 million units. And this year, the Ford Division of Ford Motor Co. expects to sell more light trucks than cars -- something that has not happened at Ford before.

In comparison to the 4.7 million trucks, the auto manufacturers sold 11.4 million new cars in the United States last year.

That's still a lot more cars than trucks, but trucks' share of the market is up dramatically. The 1985 numbers add up to about 43 light trucks sold for every 100 new cars -- compared with 17 trucks per 100 cars in 1965 and 31 trucks per 100 cars in 1975.

Ford has added capacity to build 80,000 more light trucks annually at its Kansas City, Mo., assembly plant. And the company is putting on a second shift at its light-truck plant in Norfolk, one of four U.S. sites where Ford's "F" series pickups are assembled.

General Motors Corp., Chrysler Corp., American Motors Corp. and the six Japanese companies selling light trucks in the United States also expect strong sales of those models in 1986.

The statistics for light trucks include the new minivans being offered by a number of manufacturers, which boosts the numbers somewhat, but few industry observers doubt that sales of traditional models are booming.

"I think the trend is real," analyst Peter C. Van Hull said about the growth of light-truck sales. The pattern "over the last five years shows that it is real."

On their way to trendiness, trucks have developed split personalities, becoming both inexpensive basic transportation and luxury-laden macho machines. Both personas are selling well.

Spradley and her boss, former senator Schmitt, said they believe that the rest of America is discovering what the citizens of rugged New Mexico knew all along: You can do almost anything with a light-truck-class vehicle.

"In New Mexico, a truck is a necessity because of the terrain," Schmitt said. "That open bed in the back of a pickup is very convenient," said the former senator, who even used it on occasion to cart constituents to Washington dinners.

"Many people today still talk about the time they went out to dinner with their senator in the back of a pickup truck. The truck has gotten more publicity than I have, and I enjoy it," said Schmitt, who lost his 1982 senatorial race and now spends much of his time working as a science and technology consultant.

Trucks are now available with virtually every option that can be obtained on a luxury sedan. Seventy-seven percent of all domestically produced light trucks have tinted windows. About 42 percent of those trucks come with cruise control; 28 percent have power door locks; 47 percent have some form of stereo sound equipment; 61 percent are equipped with air conditioners; 71 percent come with automatic transmission, and 94 percent have power steering, according to figures provided by Ward's Automotive Research.

In those trucks, the appeal of a multifunction vehicle is combined with a desire for the best in personal comfort, "which means that you can wind up with a pickup or a van costing $20,000 or more," said Patrick J. Keegan, general manager of Chrysler's truck division.

And the take isn't bad for the manufacturer, either, according to James E. Harbour, a Detroit-area auto industry analyst. "Light trucks have always been more profitable products for the manufacturers," because production costs for those models generally are lower than for compact cars, Harbour said.

Industry officials agree, albeit privately.

"Let's just say that we really don't mind if a guy buys a base Ford Ranger truck $5,993 manufacturers' suggested retail instead of a base Escort car $6,052 . . . because we get a little more money on the Ranger," a Ford official said.

At the same time, however, base-model, subcompact pickups generally sell for less than subcompact cars, which is spurring sales at the other end of the scale, said David Healy of New York-based Drexel Burnham Lambert Inc.

The credit for that phenomenon should go to the Japanese, according to Healy and other analysts.

Japanese trucks are not subject to the voluntary quotas that have limited shipments of Japanese cars to the United States since 1981.

Japanese manufacturers "have been shoving trucks down their dealers' throats" to increase their overall vehicle sales in this country, said Robert M. McElwaine, president of the Washington-based American International Automobile Dealers Association.

Highly competitive pricing is the direct result of Japanese aggressiveness in light-truck sales in the United States, Healy and McElwaine said.