Douglas S. Morgan is a typical research scientist: bright, inquisitive, fond of spectrometers, comfortable with chemistry's arcane lingo--an expert on electron spin resonance, as a matter of fact.

So when the 18-year-old insists there are times when he prefers a basketball court to his favorite laboratory at McLean High School, he takes pains to explain why.

"I never really pictured myself as a scientist," said Morgan, one of 40 high school students in the country named last week to the final round of the 42nd annual Science Talent Search, a prestigious science competition sponsored by the Westinghouse Electric Corp.

"Even now it's hard to assume that my whole life will be in science. I like it, but I'm no Mr. Spock," said Morgan, referring to Star Trek's cool, analytic alien. "I don't want to be that inhuman."

Morgan, son of economist Bruce W. and Barbara F. Morgan, who live in Falls Church, has been sweeping regional and state science fairs for the past two years with a sophisticated study of cancer-causing agents found in many foods, including beer and bacon, as well as certain drugs.

For years, scientists have used a heating-and-cooling technique to pinpoint the carcinogens, called nitrosamines. Morgan studied an alternate method: electron spin resonance (ESR), which can detect the carcinogen molecules as they "jump" around an electromagnetic field.

"What my project showed was that, in certain circumstances, ESR may be a more specific method of finding nitrosamines," Morgan said. "It's not a breakthrough or anything, but the FDA Food and Drug Administration , say, could apply it to a whole bunch of different things."

Becoming a finalist in the Westinghouse award--finalists each received $500 and compete for scholarships of up to $12,000 in a competition next month in the District--carries a lot of clout with college admissions officers, spokesmen for the Science Talent Search said.

It might have something to do with the contest's record of picking future stars in science: Five previous winners have won the Nobel Prize, and 21 have been elected to the National Academy of Sciences.

"It's not Hollywood or anything, but I'm flattered, really," said Morgan, who spent his high school summers at science symposiums and at training programs at American and Georgetown universities. Last year, he researched nitrosamines in beer at the FDA.

Morgan's love affair with science started at Fairfax County's Longfellow Intermediate School when the sports nut, then in eighth grade, realized "science pays you back, extracurricularly, right away."

"The thing of it was," he said, "that what I was learning in the science classroom was applicable to all this other stuff. I just lucked out."

In his sophomore year at McLean High School, Morgan took Edgar P. McConnell's honors chemistry class, one of several special programs the school offers. Advanced classes in physics, biology and calculus soon followed.

"McLean is the type of school that offers you opportunities if you seek them out," said Morgan, crediting McConnell for encouraging him to enter the science fairs that led to the Westinghouse award.

McConnell, who has been teaching at McLean for 14 years, has played mentor to three Westinghouse finalists. "I'm very demanding, very hard to please," he said last week. "But I have essentially little or nothing to do with these accomplishments. All I do is tell them what's available and then nag them to do it."

That combination of a student's own drive, a friendly teacher and a school that spares nothing to stir students' interest is typical of many of the Westinghouse finalists, said Robert Henderson, a spokesman for the company.

New York City-area schools, many of them specializing in science, are the perennial leaders in the talent search; this year, they produced a whopping 19 finalists--15 more than Florida, their closest competitor.

"It is a reflection on a school system if they have a lot of Westinghouse winners," Henderson said. "But the only secret ingredient I've spotted is hard work. These kids have incredible energy and curiosity. They get permission to use a piece of equipment at a hospital lab. They'll go meet a professor at a college."

At McLean High School, Morgan is first in his graduating class, student government president and literary magazine editor. He hopes to attend either Yale University or the University of Virginia.

He has the five-day Westinghouse finals to attend next month, then it's off to Detroit in May for another national science fair.

"I can't picture myself as an engineer," Morgan said. "I'm too non-rational for something really that technical. I want to get into some pure science first. Later, if I want to jump on a bandwagon--engineering, electronics--then maybe I could."