More ultraviolet light suppresses marine productivity in the Antarctic, according to findings of new research on the Antarctic ozone hole.

Sayed El-Sayed of Texas A&M University said this week his findings could mean the existence of a threat to the krill, a tiny shrimplike creature on which all Antarctic life depends directly or indirectly.If the krill goes, "the whole ecosystem probably would collapse," and the whales, seals, penguins, birds and fish would disappear, he told reporters at a briefing arranged by the World Resources Institute, a Washington environmental policy research institute that has called attention to ozone problems.

The ozone layer high above the earth thins by about half over Antarctica each spring, letting more ultraviolet light reach the ground. If this happened over the globe as a whole, the Environmental Protection Agency says, each 1 percent decline in ozone would mean a 2 percent increase in ultraviolet radiation and a 4.8 percent to 7.5 percent increase in the most common skin cancer.

The krill, which are an inch or two long, feed on phytoplankton, which are invisible to the naked eye. Fish and marine mammals in turn feed on the krill.

A 10 percent harvest of the 550 million to 770 million tons of protein represented by the krill could equal the entire fish catch of the world, and several nations are studying use of such a protein resource.

El-Sayed and his students at an island near Palmer Station labeled test tanks of southern ocean water containing phytoplankton, the "grass of the sea," with radioactive calcium carbonate.

The radioactivity of the plankton after taking up the carbon isotope is a measure of photosynthesis, the process by which plants live, deriving energy from sunlight.

Samples to which extra ultraviolet had been added showed far less radioactivity: 1,000 counts per minute on a scintillation counter as opposed to 15,000 counts per minute for the sample from which all ultraviolet had been excluded.

The extra ultraviolet was about 6.5 percent of what was already in the light. On the day the measurements were made, ozone overhead was only about 80 percent of normal, so the light was already presumably enriched in ultraviolet.

Ultraviolet reaching the ground in Antarctica is not as much as it would be elsewhere under the same ozone layer. The sun is low in the sky and its light travels a long slant distance through the ozone.

Scientists attribute the Antarctic ozone hole, and a newly discerned average 2.3 percent year-round ozone decline in northern mid-latitudes since 1969, to man-made chemicals called chlorofluorocarbons. Major producing nations agreed in Montreal last year to a 50 percent cut in production by 1998, and last week du Pont Co. said it planned to stop manufacture.

EPA Administrator Lee Thomas said this week the United States should seek a stronger international treaty calling for a cutback in the production of chemicals that damage the ozone layer.

But Thomas said he does not support pending legislation calling for a 95 percent cut in the production of such chemicals, known as chlorofluorocarbons, by U.S. producers.

Thomas told reporters he was against the United States "trying to move more quickly than everyone else."

"I'm very concerned that it would just take the pressure off other countries," he said.

Instead, he said, the United States should try to strengthen the existing Montreal Protocol signed last year by 31 countries, but ratified so far only by the United States and Mexico.

"We've got to keep pressure on the other countries," he said.

The proposal for a 95 percent U.S. cut in CFC production over eight years was made by Sen. Max Baucus, D-Mont., chairman of the Senate Hazardous Wastes and Toxic Substances Subcommittee.

The treaty calls for a 50 percent cut in CFC emissions over six years.

There is strong scientific evidence that CFCs are destroying the stratospheric ozone layer and allowing more ultraviolet radiation to reach the Earth, where it is expected to increase skin cancer and other health problems and to damage crops as well.

CFCs are used in refrigerators, air conditioners, solvents and in foam packaging.

Thomas said the goal was to seek negotiations for strengthening the treaty by early 1990.

In insisting that the United States should press for further reductions in CFC production in other countries, Thomas said production had leveled off in this country but was growing in others.

"That's clearly where the solution lies," he said.