Washington ? Widespread use of the hydrogen fuel cells that President Bush has made a centerpiece of his energy plan might not be as environmentally friendly as many believe.

Scientists say the new technology could lead to greater destruction of the ozone layer that protects Earth from cancer-causing ultraviolet rays.

Researchers issued a report Thursday saying that if hydrogen replaced fossil fuels to run everything from cars to power plants, large amounts of hydrogen would drift into the stratosphere as a result of leakage and indirectly cause increased depletion of the ozone.

They acknowledged that much is still unknown about the hydrogen cycle and that technologies could be developed to curtail hydrogen releases, mitigating the problem. But they say hydrogen’s impact on ozone destruction should be considered when gauging the potential environmental downside of a hydrogen-fuel economy.

Congress plans to pump more than $3 billion into hydrogen research over the next five years in hopes of putting fuel-cell-powered cars into showrooms by 2020. Industry is spending billions more to develop fuel cells, although their widespread use is probably still decades away.

Unlike fossil fuels coal, oil or natural gas which produce an array of chemicals that pollute the air as well as the greenhouse gas carbon dioxide, a hydrogen fuel cell when making energy releases only water as a byproduct.