President Bush called Friday for banning the production and use of ozone-depleting chemicals by the end of the century if adequate substitutes can be found.

His move to protect the world's ozone layer, which shields the earth from much of the sun's cancer-causing ultraviolet rays, came on the heels of a decision Thursday by 12 European countries to pursue a ban on the chemicals instead of only cutting back on production, as the world's industrial nations had earlier agreed to do.The United States accounts for about one-third of the production of ozone-damaging chemicals, primarily chlorofluorocarbons, or CFCs, which are widely used as coolants in refrigerators and air conditioners and as a cleaning agent for electronic and computer equipment.

Richard K. Reilly, head of the Environmental Protection Agency, had sought the stronger administration position on CFCs before he left Friday for London, where representatives from more than 100 nations are meeting to discuss the ozone-depletion problem.

In remarks at the National Academy of Sciences to a group of high school science award winners, Bush said "recent studies indicate the 50 percent reduction (of CFCs under existing treaty) may not be enough."

The president said he asked Reilly to join other nations at the meeting in London to support the call "for the elimination of CFCs by the year 2000 provided safe substitutes are available."

Reilly, according to administration sources, had strongly recommended at a White House meeting Thursday that the United States join its European allies and call for the complete elimination of CFCs, as opposed to cutting production by 50 percent as required by current treaty. Many scientists have said that such a cutback would not be enough to protect against serious ozone depletion.