Next year there will be a census of a different kind.

Alarmed by continuing reports that some common species of frogs are croaking their final croaks, baffled scientists will survey the world's frog population."Something is going on and we need to find out what it is," said Steve Hammock, an official of the Fort Worth Zoo and chairman of the North Texas Herpetologists Society.

At an international meeting this summer, scientists concluded that many of the world's common species aren't merely declining, they have become extinct in large parts of Europe, Canada, the western United States, Mexico and Central and South America.

Hammock and other biologists are devising standard survey forms for distribution to professional scientists and amateur naturalists who will be asked to monitor local frog populations.

The survey project, whose data is to be collected by the University of Kansas, grew out of the meeting of more than 400 scientists in New Orleans.

Organized by John Wright, curator of herpetology at the Natural History Museum in Los Angeles, it was one of several meetings called by worried scientists since the mystery was first discussed by biologists in Great Britain in the fall of 1989.

"We know that amphibians are among the better biological indicators of environmental degradation," Wright said. "Their disappearance tells us the world could be in serious trouble."

Frogs and other amphibians are environmental barometers for several reasons. They are high in the food chain and integral to many ecosystems. Their total numbers often are huge and, throughout their life cycles, their skin remains permeable to water and whatever affects it.

Among suspected causes of the extinctions: depletion of the atmosphere's ozone shield against deadly ultraviolet radiation from the sun, toxic heavy metals from acid rain, worldwide proliferation of pesticides and other environmental pollutants.

The New Orleans meeting, including participants from the 2,000-member Society for the Study of Amphibians and Reptiles and the 1,100-member Herpetologists League, concluded that the extinctions are not occurring in polluted developed areas but in pristine national parks, private preserves and wilderness areas.

"The higher elevations are where there are severe declines if not outright disappearances," said William Brown, president of the Society for the Study of Amphibians and Reptiles and a professor of biology at Skidmore College in Sarasota Springs, N.Y.

"It looks like almost anything at high elevation is in trouble, and those are the (species) we know the least about," Wright added. "Some of our colleagues are pretty convinced it's related to increased ultraviolet radiation at higher elevations."