Girls won top honors for the first time last week in the Siemens Competition in Math, Science and Technology, one of the nation's most coveted student science awards, and contestants from the Philadelphia region got plenty of notice.

Isha Himani Jain, 16, a senior at Freedom High School in Bethlehem, Pa., placed first in the individual category for her studies of bone growth in zebra fish, whose tail fins grow in spurts, similar to the way children's bones do. She will get a $100,000 scholarship.

Janelle Schlossberger and Amanda Marinoff, both 17 and seniors at Plainview-Old Bethpage John F. Kennedy High School on Long Island, split the other $100,000 top prize, in the team category, for creating a molecule that helps block the reproduction of drug-resistant tuberculosis bacteria.

The girls' victories are "wonderful news, but I can't honestly say it's shocking," said Nancy Hopkins, a biologist at the Massachusetts Institute of Technology.

Hopkins helped start a national discussion about girls and science two years ago when she walked out of a talk by Harvard University's president, Lawrence H. Summers, after he suggested that innate differences between men and women might be one reason that fewer women than men succeed in math and science careers. Summers apologized during the ensuing furor; he announced his resignation as Harvard's president 13 months later.

"Why do people think girls can't do science?" Hopkins said last week. "Where did this crazy idea ever come from?"

James Whaley, president of the Siemens Foundation, which oversees the competition for Siemens AG, a global electronics and engineering company, said the competition results sent a great message to young women.

It certainly did for three homeschooled girls from both sides of the Delaware River near Trenton.

When their team - Caroline Lang of Yardley and Naomi Collipp of Levittown, both 16, and Rebecca Ehrhardt, 15, of Hamilton Square, N.J. - gave the required 12-minute presentation last Sunday, they used a Power Point presentation to demonstrate their "Burgercam" monitoring system.

The Burgercam is designed to determine when E. coli bacteria in hamburgers have been safely eliminated by measuring the shrinkage of each patty when fully cooked.

Several hundreds of hamburgers later, the girls took home fifth place nationally and split $20,000 in scholarship money.

Caroline, Rebecca and Naomi, called "the Hamburger Girls," said they had been friends since they were toddlers and had stayed in touch through a group for home-schooled children.

"They were concerned it wasn't sophisticated enough, but they wanted to try," said Rebecca's mother, Alicia Butcher Ehrhardt, a plasma physicist.

More than 1,600 students nationwide entered the Siemens competition. After several rounds of judging by a panel of scientists led by Joseph Taylor, winner of the 1993 Nobel Prize in physics and a professor emeritus at Princeton, 20 finalists were chosen. They presented their projects at New York University and vied for scholarships ranging from $10,000 to $100,000.

Eleven of the finalists were girls - the first year that girls outnumbered boys in the finals. Most of the finalists attend public school. Three-quarters of them have a parent who is a scientist.

Isha Himani Jain, who took the top individual prize home to Bethlehem, published her first research paper with her father, a professor at Lehigh University, when she was 10 or 11; her mother is a doctor.

Isha said she chose to study zebra fish - work that she has already published in the journal Developmental Dynamics - because they are a good animal model.

"They're simple creatures, and if you amputate their fins they regenerate," she said.

She said her research should lead to understanding bone growth in other vertebrates along with bone disorders in humans.

At last week's awards ceremony, Isha teared up during her brief acceptance speech, then ran and jumped into her father's arms.