Students from a Manhattan elementary school were frolicking in the surf at an unguarded Long Island beach while a girl from another city school drowned there, sources said yesterday.

Fifty-one children from PS 3 in the West Village were on a trip to Long Beach when Nicole Suriel, 12, a sixth-grader from Columbia Secondary in Harlem, was dragged under, the Department of Education said.

Teachers got the PS 3 kids out of the water when they learned the girl was missing, said Natalie Ravitz, a DOE spokeswoman.