A new study has found that high school students whose teachers have emergency teaching certificates -- typically issued by states to meet shortages in the classroom -- perform about as well in mathematics and science as students whose teachers hold regular teaching credentials.

The surprising finding, based on the test scores of a national sample of high school seniors and sophomores, runs contrary to the assumptions of a Clinton administration proposal to require states to stop issuing emergency teaching certificates as a condition for receiving federal education aid. After President Clinton called for such a ban in his State of the Union address this year, the administration in May proposed giving states four years to dramatically scale back emergency certification of teachers.

"Contrary to conventional wisdom, mathematics and science students who have teachers with emergency credentials do no worse than students whose teachers have standard teaching credentials, all else being equal," Dan D. Goldhaber and Dominic J. Brewer concluded in their contribution to "Better Teachers, Better Schools," a report released yesterday by the Thomas B. Fordham Foundation.

Other findings made by Brewer and Goldhaber -- a labor economist who serves on Alexandria's school board -- underline the importance of teachers specializing in the subjects they teach. The study concluded that students whose teachers have college degrees in math or have been specifically certified to teach math score significantly higher on standardized tests than students whose teachers did not specialize.

The new study appears likely to stimulate debate about the best ways to improve teacher quality, widely regarded as central to raising student achievement levels. It is expected to be a tough challenge to improve the quality of teachers at the same time that the nation hires more teachers because of record enrollments, an anticipated wave of retirements and moves to reduce class sizes in the earliest grades.

The Education Department estimates there are about 50,000 teachers with emergency certification, meaning they have been exempted from state standards on education courses, practice teaching and professional exam scores. Locally, Goldhaber said, the practice is most common in the District and Prince George's County.

Therese Dozier, teaching adviser to Education Secretary Richard W. Riley, said other studies conducted in Florida and Texas support the administration's opposition to emergency certification. "The research that I have been familiar with says training does make a difference," she said.

Goldhaber acknowledged that more research was needed on the quality of emergency certified teachers hired in recent years because the data he used were collected seven years ago, before the number of such hirings jumped significantly.