At the age of 3, Stacy Marcus used to concoct scientific "potions" in a bathroom sink by mixing the contents of her parents' medicine cabinet. At 9, she went to a summer camp that specialized in model rocketry.

Now 16, she is preparing for a taste of science more tantalizing than even she had imagined: a year-long apprenticeship alongside a researcher at the National Institutes of Health.

"It is like getting a glimpse into my future," said Marcus, an honors student with a 4.0 grade average at Silver Spring's John F. Kennedy High School. She is thinking of a career in medical research or biomedical engineering.

She is one of 11 students and a few dozen teachers who will benefit from a novel gift to Montgomery County's public schools.

The gift consists of two grants, totaling $253,000, from the Howard Hughes Medical Institute, the nation's largest private sponsor of medical research. They are the first grants that the institute, which typically subsidizes professionals and graduate students, has given directly to a public school system.

At a news conference yesterday, the institute's leaders said that, in branching out to younger students, there is self-interest.

"What we're talking about today is the beginning of a scientific pipeline," Purnell Choppin, the institute's president, said in a chemistry lab at Kennedy High where the gift was announced.

Of 4 million 1977 high school sophomores who indicated an interest in scientific careers, 5 percent kept those plans through their senior year in college and 0.2 percent eventually earned a PhD, according to a recent National Science Foundation study that Choppin cited.

"There are just a few drops coming out of the end of the pipeline," he said, noting that women and members of minority groups are particularly underrepresented.

At the same time, a variety of groups has called lately for revisions in science education to include more science instruction and a curriculum that stresses experiments.

That is the premise behind the Hughes Institute gift. One grant will help teach high school biology teachers throughout Montgomery about recent research into biotechnology and DNA. For the next three years, a van, stocked with sophisticated biotechnology equipment, will travel to the county's high schools. Teachers also will attend workshops on molecular genetics and the way scientific advances are applied in law, medicine and farming.

The other grant will finance the apprenticeships, in which the students and one teacher each from Kennedy and Gaithersburg high schools will spend six weeks this summer at NIH. They will continue their research four half-days a week throughout the coming school year. On the fifth day, they often will visit county elementary schools, talking about science and performing experiments for young children.

According to Michael Fordis, director of the institutes' office of education, students will help explore how normal cells become cancerous, which proteins affect behavior, and how genes control development, among other projects. Tania Moss, a Gaithersburg sophomore, said that until now, her most sophisticated scientific encounter has been examining the inside of a starfish, a project she described as "pretty gross but really interesting."

"This will be a proving ground to see whether I want to be a doctor," Moss said.