The ozone layer protecting Earth from cancer-causing ultraviolet radiation is being destroyed about twice as fast as was previously believed, the government says.

The depletion is particularly severe over the United States, according to findings that one Environmental Protection Agency official Thursday called "pretty shocking."The increased pace of ozone depletion could mean an additional 200,000 deaths from skin cancer in the United States over the next 50 years, EPA Administrator William K. Reilly said. That would be a near-doubling of the current rate of 5,000 skin cancer deaths annually.

"These data suggest depletion of 4 to 5 percent has occurred since 1978 over the United States," Reilly said. "Past studies had shown about half that amount."

"What's happening is close to the worst fears," said F. Sherwood Rowland, a chemistry professor at the University of California, Irvine, who discovered in 1974 that chlorofluorocarbons, or CFCs, were damaging the ozone layer.

Reilly said the EPA would step up efforts to halt production and use of CFCs and other industrial chemicals blamed for ozone depletion.

The new data on ozone came from global satellite monitoring begun in 1978. Rich McPeters, chairman of the ozone processing team at the National Aeronautics and Space Administration's Goddard Space Center, said details would be set out in two papers, one already submitted for publication and one still being revised.

The studies found a global decrease of 2.6 percent over 10 years, he said, with the effects concentrated in the middle latitudes of the Northern and Southern hemispheres.

"If you look at the equator, there's nothing happening," McPeters said. "Above 20 degrees latitude north or south, you start seeing some very large decreases."

At 40 degrees north latitude - which cuts through the middle of the continental United States - ozone has been disappearing at a rate of about 0.5 percent per year, McPeters said.

"These are shocking numbers," said Eileen Claussen, director of EPA's atmospheric and indoor air programs.

Claussen said helping developing countries reduce their emissions of ozone-depleting chemicals was "the biggest thing that can make a difference."

In addition, she said, EPA can encourage recycling of the chemicals - found in car air conditioners, for example - and can make sure that any substitutes developed are not ozone-destroying themselves.

A new cause for concern, Claussen said, is that while older studies found ozone depletion mostly in winter, the new data find a thinning layer in the spring as well, when plants are growing and people are more likely to be outdoors.

"This new data is very frightening," said Liz Cooke, ozone campaign director for the environmental group Friends of the Earth.