Conferees Optimistic About New Ozone-Layer Controls : Environment: A U.S. shift on funding is seen as removing a key obstacle to a stronger pact.

An international conference to stave off further erosion of the Earth’s protective ozone layer opened here Wednesday amid widespread optimism that an agreement is near to significantly strengthen controls on ozone-destroying chemicals.

Delegates from more than 55 nations and from major chemical manufacturers and environmental groups closeted themselves to hammer out details of far-reaching amendments to the Montreal Protocol, which will expand the list of chemicals controlled by the accord and establish a fund to assist Third World nations in paying for more expensive ozone-friendly substitutes.

The negotiations, expected to continue at least through Saturday, are aimed at presenting a final document to environmental ministers for their endorsement when they arrive next week. Their endorsement would precede formal approval by their governments.

“We cannot afford to fail in London. The stakes are very high,” Mostafa K. Tolba, executive director of the United Nations Environment Program, told participants shortly before the conference was closed to the public.

Stressing that the threat is global, Tolba added: “It is a must that north and south, east and west should cooperate together. It is not an option.”

The stratospheric ozone layer shields all life on the planet from the sun’s ultraviolet radiation, which can cause skin cancer, cataracts, suppression of the body’s immune system and damage to plant and animal life.

Only a week ago, there was considerably less optimism that an agreement on strengthening the protocol could be achieved. Last month, at a preliminary U.N.-sponsored meeting in Geneva, the United States served notice that it would oppose any effort to require industrialized countries to provide additional aid to Third World nations to help them pay the higher costs of using less harmful chemicals. It argued that the World Bank has sufficient funds to meet the needs.

The U.S. position stirred an international outcry, not only among Third World countries sometimes referred to as “the South” but even from Americas’ closest allies. They urged President Bush to reverse the position, which was fashioned by White House Chief of Staff John H. Sununu and Richard Darman, director of the White House Office of Management and Budget.

Late last week after intensive lobbying, Sununu told reporters that the United States will now support additional funds and offered a proposal for dispensing them.

The latest U.S. plan is not totally acceptable to developing countries, who want a greater voice in spending the estimated $240 million needed in the first three years of the program. Nor is there agreement on how developed countries such as the United States are to be assessed their share of the contributions.

Still, there was general agreement here Wednesday that the biggest obstacle has been overcome.

“That has removed what many people regarded as a major obstacle to this meeting, and we are grateful for the shift,” British Environmental Secretary Chris Patten said of the U.S. shift. British Prime Minister Margaret Thatcher was one among those who urged Bush to reverse course.

Another encouraging sign came Wednesday when delegates from China presented an estimate of their cost for complying with the protocol which closely matched Tolba’s--about $40 million in the first three years.

Neither China nor India, which together account for 40% of the world’s population, has signed the protocol. At a similar ozone conference here last year, they warned that unless developed countries, which they blame for most ozone depletion, foot much of their costs, they will not sign.

Several major amendments to the protocol are under consideration. They include a total phase-out of ozone-destroying chlorofluorocarbons (CFCs) by the year 2000 instead of the 50% reduction called for in the original protocol signed three years ago.

The original accord also limited the consumption of halons--used as fire extinguishing agents--only to 1986 levels, starting in 1992. The proposal now before delegates calls for a 50% reduction by 1995 and a ban by the year 2000. The United States and the European Community have endorsed the earlier schedule.

At the same time, two chemical solvents that contribute to ozone depletion but are not now covered by the protocol are expected to be added: carbon tetrachloride and methyl chloroform.

Even as the conference opened, delegates were given disturbing additional evidence of destruction of the ozone layer. A report released by British government said recent evidence has reinforced a 1988 report of “substantial damage” to the ozone layer.

They said that the ozone hole over the Antarctic was “depleted as severely” in 1989 as it was in 1987. The report said that the less severe depletion in 1988 “was not a sign of recovery” but merely evidence that variability from year to year should be expected.