Stephanie Ann Telesetsky, a poised 16-year-old from Rockville, has been named one of the most promising scientific talents in the country by the Westinghouse Science Talent Search.

Telesetsky was among 40 finalists who met in Washington last weekend to compete for 10 scholarships totaling $74,500. Although she did not win one of the scholarships, Telsetsky received a $500 award.

Making it to the finals is one of the most prestigious honors a high school senior can earn. In recent years the competition has been nicknamed the "Nobel Farm Club" because five former winners have gone on to receive Nobel Prizes in the past decade.

The finalists were chosen from nearly 1,000 students from across the country and American schools overseas.

Telesetsky, first in her senior class at Stone Ridge School in Bethesda, was chosen for her work on the cell mechanism that resists certain antibiotics in several strains of E. coli, a bacterium that lives in the human gut.

The climax of the competition came last weekend when Telesetsky and the other finalists came to Washington for banquets and lectures, meetings with Vice President George Bush and members of Congress, and the final judging--several days of grilling by eight scientists who would determine the most talented.

On Friday, Telesetsky was in the midst of the hubbub in the Great Hall of the National Academy of Sciences. Excited young people darted back and forth, carrying boxes, borrowing tape, trying to get the exhibits of their science projects up for the large audience expected.

Telesetsky, with sandy hair and glasses, hands thrust in her down vest, watched her colleagues calmly.

Earlier in the day Stephanie slipped and hit her head on a table while she was watching an operation at the National Zoo hospital, and spent most of the afternoon in the emergency room getting seven stitches. She didn't mention it during the interview. Her attention focused instead on the competition.

Despite her control and professional manner, Telesetsky is exuberant when she talks about the Westinghouse competition.

"It's an incredible honor. I was flabbergasted," she said. "I didn't know what to say" when she learned that she was a finalist. Then breaking into a grin, "For somebody like me (who has no difficulty with speechlessness), that's a real surprise."

Her parents, Sharron-Dawn and Walter Telesetsky, were equally surprised. When she called her father, who is chief of operations at the National Weather Service, "He asked me if I had written proof. He didn't believe it till he got the letter."

Walter Telesetsky said that over the years he had been invited to the Westinghouse winners' exhibits many times along with other scientists. "Each time I go I am constantly amazed at the level of ability of these students.

"I just wish she hadn't bumped her head. She wasn't feeling too well when she went through the interview with the chairman of the science committee," he said. "But as far as I'm concerned, she's a winner no matter what."

At 16, Stephanie Telesetsky has amassed more honors than most adults twice her age. In addition to being a straight-A student, she is a Distinguished Maryland Scholar, an honor conferred by the state to National Merit Scholarship finalists who have exceptionally high grades; the winner of an Army medallion for outstanding achievement at the Montgomery Science Fair; and the captain of the school's team for It's Academic, a local television competition for high school scholars, and her school's forensic League. She holds 11 swimming records.

Her ability with both language and science developed when she was very young, her father said.

When she was 3, she was enrolled in a Montessori school, where students advance according to their abilities. Almost immediately, she began working with students several years her senior. "Our only concern was social adjustment," said her father, "but it just never was a problem."

Stephanie skipped fifth grade and entered sixth grade at Stone Ridge.

Because of her high scores on national achievement tests that year, she was enrolled in the Johns Hopkins University program, Study of Mathematics for Precocious Youth, which has led to several other opportunities and college courses for the gifted.

"In the sixth grade, she did a project on molds that I thought would be fairly simple," Mr. Telesetsky said. By the time Stephanie finished her study, she wrote an exhaustive 70-page report detailing the growth of molds in every type of condition.

That kind of persistence also distinguished her work for the Westinghouse competition. Her project began last summer, when she was working as a biological aide at the National Institutes of Health under Dr. Loretta Leive.

Telesetsky spent 45 hours a week trying to figure out what makes the outer membrane of some bacteria resist certain antibiotics that are fat-soluble, a significant problem in medical research. "Every now and then I'd get to eat lunch," she said. "I'd think, 'Well, I'm starving to death, but I can't leave my cells.' "

Dr. Leive was impressed with both her enthusiasm and her approach. "She is very much like a real scientist in that she's always trying to think out what went wrong and what nature is trying to tell you."

After several months of work, Telesetsky found that some mutant strains of bacteria were allowing tetracycline into the cell, which suggested that there had been a change in the cell's outer membrane.

Telesetsky would like to study biology at Princeton University, and eventually become a doctor. She has already been accepted there, but her final decision will depend on financial concerns. She estimates it will cost $12,000 a year to attend Princeton. With the university's policy of not giving academic scholarships and the difficulty of getting student loans, Mr. Telesetsky said it will be hard to pay for a Princeton education, even though he makes a good salary.

Although she could skip her freshman year in college, Stephanie said she has decided not to. "I just don't want to rush it," she said. "You're really under a lot of pressure."

Mr. Telesetsky would like his daughter to take a "smorgasbord" of courses before she commits herself to medicine. He says she tells him "if she becomes a doctor, she will go off and tend the poor, wherever they are."

She has such a strong sense of social responsibility, he added, that she takes time from her studies to take orphans shopping at Christmas, and to be a hugger at the Special Olympics for retarded children.

She is equally adamant about not being labeled precocious. "I don't see it as a major burden keeping me away from my peers," she said. "I like to do what everybody else does, I swear I do." In fact, she adds, the only drawback at Stone Ridge, a private girls' school, is that "it makes it harder to be good friends with guys."