Coral reefs around the world, which biologists say may serve as an early warning system for environmental degradation, are suddenly starving and in many cases dying because of abnormally warm seas, according to leading marine scientists.

The phenomenon, which has occurred three times in the 1980s, may be more serious this year. Coral reefs are blotchy and sickly in many locales, including the Florida Keys, Puerto Rico, Jamaica, the Bahamas, Bermuda, Hawaii and Okinawa, Japan. Researchers say more reports of damage will probably trickle in over the next few months.

Most researchers suspect the current crisis is caused by higher sea temperatures. As the water heats up, the coral polyps that build the reef with their skeletal remains spit out the microscopic algae that help feed the coral and give the reef its golden, red and yellow hues. The phenomenon is called "bleaching" because it leaves the coral with white blotches. Without its algal partner, the coral becomes weak and stops reproducing. After several weeks, it may die.

"Our reefs are in peril and are disappearing at an alarming rate," said Robert Wicklund of the National Oceanic and Atmospheric Administration's Caribbean Marine Research Center.

"We are getting very concerned that this is happening with greater frequency," said Walter Jaap of the Florida Department of Natural Resources. In many cases, we're seeing the corals don't recover." In past episodes, the corals would often return to health. But there is preliminary evidence that repeated stress may make recovery more difficult.

While the marine biologists suspect the corals are being damaged by higher sea temperatures, they are unsure whether the phenomenon is a natural one caused by periodic changes in sea currents, such as the cyclical El Nino ocean upwelling in the Pacific, or whether the planet is warming because of an enhanced greenhouse effect caused by a buildup of pollutants.

At a hearing yesterday on the coral damage before the Senate Committee on Commerce, Science and Transportation, chaired by Sen. Albert Gore Jr. (D-Tenn.), Philip Jones of the University of East Anglia in England reported that 1990 will almost certainly be the hottest year on record. This year has been abnormally warm throughout the Northern Hemisphere, particularly in March, when temperatures in Sibera, Canada and West Africa were as much as 18 degrees Fahrenheit above normal. The 1980s were the warmest decade in the last 100 years.

Researchers in general agree that the Earth on average has warmed by about 1 degree Fahrenheit in the last 100 years. Many climate experts predict that temperatures will increase several degrees in the next century, as greenhouse gases such as carbon dioxide and methane accumulate in the atmosphere, where they act like a blanket to trap heat. However, the exact timing and magnitude of worldwide warming is vigorously debated by scientists.

Many marine biologists believe that the coral bleaching is a sign that the delicate reef ecosystems are suffering from stress. Some suggest that the bleaching episodes are the first biological effect of global warming, and that like canaries in a coal mine, the reefs are a danger signal.

"The first proof of global warming may come from the bleaching of corals," said Ernest Williams of the University of Puerto Rico. But Williams said that not enough is known to conclude that this is the case.

Until the worldwide bleaching episode of 1987, the periodic phenomenon was "virtually ignored," Williams said. He and his colleagues found that there was also widespread bleaching in 1979-80 and 1982-83. There have been isolated reports of bleaching since 1911, though only in recent years have the episodes been so widespread. In addition to higher temperatures, coral reefs may be harmed by pollution, changes in salinity and silt deposits.

Beginning last year, Thomas Goreau of the Discovery Bay Marine Laboratory in Jamaica began to detect bleaching along the entire northern shore. Bleaching is also extensive in the Bahamas and parts of the Florida Keys.

"Like most of my colleagues, I am deeply alarmed at these trends," Goreau said. "If they continue, many coral reefs will cease to be viable in coming years."