Chalk one up for the public school kids.

In a recent citywide mathematics contest, the District's Deal Junior High School finished in first place, beating four prestigious and expensive private schools: National Cathedral School for Girls, Sidwell Friends, St. Anselm's Abbey and Maret.

To some, it may seem like just another school contest. But in a city where parents of public school children are routinely on the defensive over the quality of their schools, Deal's victory is being touted as a big triumph of public education over private.

"Everyone assumes that you can't get a good education here in a public school," said Delabian Rice-Thurston, executive director of Parents United for the D.C. Schools and the mother of a student at Deal. "So every time our schools do as well or better than private schools, we are just beaming."

District public school students consistently test below national norms on standardized exams in reading and mathematics. In the last 15 years, the D.C. school population has dropped by more than 20,000, with many parents enrolling their children in private or parochial schools.

President Clinton added fuel to the debate when, for what he said were personal reasons, he chose Sidwell Friends over Deal or any other public school for his daughter, Chelsea.

Deal's victory occurred in the MathCounts competition for seventh- and eighth-graders, sponsored locally by the D.C. Society of Professional Engineers. The contest involved answering difficult mathematical questions quickly, sometimes with calculators and sometimes without.

Nick Williams, of Sidwell, had the highest individual score, but Deal's four-member team -- Brent Yorgey, Matt Ferlo, Daniel King and Adam Rapp -- came in first. National Cathedral placed second, Sidwell third, St. Anselm's fourth, Maret fifth and another D.C. public school, Jefferson Junior High, came in sixth. Paul Gilden, a math teacher at St. Anselm's, said he wasn't surprised by Deal's victory.

"I think the smartest kids in the public schools are as smart as the brightest kids in the private schools," he said.

When the Deal team pulled ahead to snatch first place, the crowd went wild, said Deal algebra and geometry teacher Guy Brandenburg.

"The parents were really pumped up," he said. "They were mighty happy."

So was the prize-winning team.

"I think it was great we were able to win, because everyone thinks that all those private schools are supposed to be where all the smart students go," said Brent Yorgey, 15, a seventh-grade who was Deal's top scorer. "Being able to beat them was exciting.

But it was not a fluke, said Laura Anthony, co-president of the PTA at Deal, which is in the Northwest Tenleytown neighborhood.

"Deal students do well all the time in competitions that involve public and private schools," said Anthony, whose son attended Deal and whose daughter is enrolled there now. "But generally speaking, the press coverage of public schools is negative. It gets discouraging. We know we've got great kids that can do well." A new team composed of the four highest scoring students, one from Deal and the others from Sidwell, St. Anselm's and Jefferson, will participate in the national competition April 27-30 at the Omni Shoreham Hotel. Staff writer Valerie Strauss contributed to this report. CAPTION: Deal Junior High student Brent Yorgey, 15, agonizes over a problem while studying for the national MathCounts competition beginning April 27.