Stepping Up to the Ozone Challenge. CLEARING THE AIR

ANXIETY about deterioration of the earth's ozone layer is prompting unusual international cooperation to curb chemical pollution of the atmosphere. Representatives of 124 nations heard pleas from scientists and government ministers at a London meeting this week to accelerate the phase-out of chemical substances that break down the thin layer of ozone protecting the earth from ultraviolet radiation.

The European Community set the pace. Its environment commissioner, Carlo Ripa di Meana, told the conference that the EC could eliminate the use of chemicals harmful to the ozone by 1996 or 1997. This is three to four years ahead of targets set last week, when the EC, in a surprise move, pledged to eliminate 85 percent of chlorofluorocarbon (CFC) usage as soon as possible and to impose a complete ban by the year 2000.

President George Bush has also announced that the United States is committed to a ban on the offending chemicals - mainly the family of compounds known as CFCs as well as halons - by the end of the century, pending the availability of safe substitutes that industry is pushing to develop. Canada and several Scandinavian countries have set similar goals.

``The world community has a strong sense of urgency about this problem, and we are now dealing with it with the seriousness it deserves,'' said William Reilly, head of the US Environmental Protection Agency.

The US is the world's largest producer and consumer of CFCs. Several US senators have introduced legislation in Congress that would compel a phase-out well before the year 2000.

But experts say that even if the Western industrialized countries, which account for 70 percent of CFC usage, do carry out such a ban, world usage of CFCs will continue to grow unless the developing countries as well as Japan and the Soviet Union cooperate.

Mr. Ripa di Meana said that developing countries need financial and technical assistance to help them make the transition to ozone friendly substances, and he proposed that Western Europe use its trade pact with African countries, the Lom'e Convention, as one mechanism of assistance.

WITH almost 40 percent of the world's population, China, India, and Brazil now account for about 2 percent of CFC usage. Scientists are concerned that as these countries industrialize and improve their standard of living, their consumption of CFCs - widely used in aerosol sprays, refrigerators, air conditioners, and as a foaming agent in insulation - could overtake the amounts now used by developed countries.

British Prime Minister Margaret Thatcher told the meeting that the need to protect the ozone layer was not a case of some countries asking others to act. ``It is a case of every country taking action if we are to protect all peoples,'' she said. She said that the London meeting demonstrated the urgency of the problem and that ``no one can opt out.''

Growing public awareness of the threat to the ozone layer has pushed many governments to affirm their support for a United Nations agreement, known as the Montreal Protocol, which pledges a 50 percent phase-out of CFCs by the year 2000. This week 20 more countries announced their endorsement of the agreement, bringing the total number to 53, and over a dozen others have indicated they probably will sign.

However, most countries at the London meeting had not signed the protocol, and scientists now say that the agreement, drafted two years ago, is no longer adequate to prevent the rapid depletion of the ozone layer. Attention is now focused on a meeting in Helsinki in May to strengthen the protocol's provisions and to take the first steps toward its implementation. There will be a follow-up meeting in London in April 1990.

The rush to save the ozone layer is a reaction to the findings of research conducted primarily by British and American scientists. In 1987 a British Antarctic Survey station reported an ``ozone hole'' over the Antarctic showing that 97 percent of the ozone was depleted over a six-week period during the seasonal peak of the ozone's formation. Another international survey this year showed that concentrations of ozone-destroying CFCs over the Arctic region were 50 times greater than predicted, suggesting there could also be an ``ozone hole'' over the North Pole.

``The present pollution of the atmosphere is a fact we will have to live with for all of the 21st century,'' said Sherry Rowland, an atmospheric scientist with the University of California at Berkeley, who first sounded the warning about ozone depletion a decade ago.