A Montgomery County high school senior and a student at the District's School Without Walls were among 40 national finalists named yesterday in a prestigious science competition, marking the first time since 1970 that a D.C. public school student has attained that status, contest organizers said.

Sabrina C. Snell, 17, who attends the senior high in downtown Washington, and Anatoly Preygel, 17, of Montgomery Blair High School, will compete against finalists from 14 states for the top prize in the Intel Science Talent Search: a $100,000 scholarship. There are no finalists from Virginia. Winners will be announced March 11.

Snell spent three years doing research for her project, which used satellite data, available on the Internet, to investigate anomalies in star motion measurements. Doing much of her research at the U.S. Naval Observatory, Snell assessed linear and accelerated motions in double stars.

Her success in the competition "shows that public education does work" in the District, she said. "I was motivated by a number of teachers in the D.C. public school system."

Preygel completed a math project on knot theory, which examines closed curves in three-dimensional space and has possible applications in physics, chemistry and genetics.

Becoming an Intel finalist was "something I couldn't believe," said Preygel, whose family moved from the former Soviet republic of Moldova to the United States in 1991. "I didn't think I'd get this far; I'm still waiting to read it somewhere, just to be sure."

The science contest, which started in 1942 and has been sponsored by Intel since 1998, recognizes students who go beyond the classroom to develop their skills in science. Snell and Preygel were among 1,581 applicants nationally, and Snell is the first finalist from D.C. public schools since a student from Wilson Senior High was a finalist in 1970, said Clint Tanner, a spokesman for Science Service, a nonprofit group that promotes science literacy and runs the contest.

Snell, the daughter of a writer and an interagency liaison at the National Institutes of Health, said her interest in astronomy was an outgrowth of trips she took with her family to NASA's Goddard Space Flight Center and from launching model rockets at a park in Anacostia.

When she was in the eighth grade, she said, she worked on a science fair project in which she researched stars and planets outside the solar system. One of the judges of that competition worked at the Naval Observatory, and he became a mentor for Snell. For the past four summers, she has worked as an intern at the observatory.

The principal of School Without Walls, Dana Bedden, said Snell ranks first in a class of 65 at the 365-student school.

Bedden said the school is poorly equipped for science and that "all we could do as a school was to continue to support her and encourage her."

The school's approach is to use the city as a classroom, sending students to the National Zoo, the U.S. Holocaust Memorial Museum and other places to learn from hands-on experience. A number of students at the school -- including Snell -- take classes at George Washington University or on other college campuses.

Preygel said last night that he conducted his first big math project in seventh grade, under the tutelage of his grandfather. Two of his grandparents are mathematicians, and both of his parents have degrees in genetics and applied mathematics.

Preygel worked with a mentor at the Research Science Institute over the summer, when he began work on his project. He plans to study math and computer science at the Massachusetts Institute of Technology and to become a math professor.

Snell said she is waiting to hear from colleges. She wants to earn a doctorate in either astronomy or anthropology.

Snell's mother, Mary Gant, said she always encouraged her daughter to develop her math skills.

"You have to understand how hard she's worked to get where she is," Gant said. "She has worked many, many, many long hours. It wasn't just, 'Oh, I'm going to have a science fair project.' "

Staff writer Petula Dvorak contributed to this report.

Sabrina Snell, 17, a student at the School Without Walls, will compete against finalists from 14 states for the top prize.