LONDON, JUNE 27 -- The United States came under strong criticism today from environmental activists and Third World states, who charged that Washington and some other industrialized nations were delaying agreement to accelerate a world-wide ban on chemicals that deplete the earth's protective ozone layer.

The dispute, which surfaced on the opening day of a three-day conference of delegates from more than 100 nations, focused mainly on a timetable under which governments would agree to phase out use of some of the chemicals and the nature and amount of aid industrialized nations are willing to give developing countries to help with phaseout there.

The delegates hope to hammer out a new agreement strengthening the Montreal Protocol, the 1987 treaty regulating substances that harm the stratospheric ozone layer, which shields earth from the sun's ultraviolet rays. They particularly want to speed up a ban on chloroflurocarbons (CFCs), which are widely used as refrigerants and cleaners, following fresh evidence that these gases and related chlorine-based chemicals are heavily damaging the ozone layer.

William K. Reilly, administrator of the Environmental Protection Agency, told the conference that the United States is committed to a 20 percent phaseout of CFCs by 1993 and full elimination by 2000 -- the compromise position proposed by the U.N. Environment Program, which is overseeing the meeting. Washington also supports a 50 percent reduction by the end of the century in the use of methyl choloroform, an industrial solvent that also contributes to ozone depletion. Reilly stressed his "heightened sense of urgency," noting that "even if we succeed in our ambitious efforts to phase out ozone-depleting chemicals, {they} will continue to destroy stratospheric ozone long after we all are dead."

But critics here complained that the U.S. timetable is too slow, and environment ministers from West Germany and Canada committed their countries today to phasing out CFCs by 1997, three years before the American deadline.

David Doniger, senior staff attorney for the Washington-based Natural Resources Defense Council, said the U.S. timetable, if adopted here, would permit more than five times the 1986 production level of CFCs to be manufactured before the final phaseout -- twice as much as under the more stringent schedule suggested by the West Germans. Because of the chemicals' stability, the extra CFCs would linger and continue to damage the earth's atmosphere for up to 80 years, Doniger said.

Eileen Claussen, director of atmospheric programs for EPA, called the push for a 1997 deadline "a political gambit" by countries assured that the United States and Japan would block such a move. She said evidence suggested that if CFCs were banned too quickly, new chemicals designed to replace them might prove equally harmful to the environment and less energy efficient.

But Australia's environment minister, Ros Kelly, whose country faces a major increase in the incidence of skin cancer because of a hole in the ozone layer that scientists have discovered in the Antarctic, said the 1997 deadline could work with U.S. support. "If a big country like the United States took the lead in endorsing a phaseout by 1997, industry will respond," Kelly said. "They could meet the target."

Reilly came to London with one major controversy eliminated after successfully lobbying the White House to drop its opposition to creation of an international fund to aid developing countries eliminate ozone depleters. The fund, currently pegged at $160 million over a three-year period, is considered essential to enlist the support of Third World states, such as China and India, which so far have refused to sign the 1987 pact. The United States is expected to contribute $40 million.

But several issues remained. Some countries opposed U.S. insistence that it be granted a permanent seat on the 17-member body that would administer the fund because it would be by far the largest donor. A more nagging issue is the question of how far the industrialized states are willing to go in transferring technology to Third World countries to help them develop and manufacture their own ozone-friendly products.

"Our phasing out of CFCs depends on the arrival of technology," said Maneka Gandhi, India's environment minister. "After all, the Third World didn't create the problem. It was created by the West, and you need to pay for cleaning it up. India will sign when these conditions are fulfilled."

EPA'S Claussen said Third World states had come to the conference with the unrealistic hope that industrialized nations would require their companies to pass on technology on a "preferential and non-commercial basis." She said also that these countries had insisted on language that would allow them to abrogate the treaty unilaterally if they believed they had not received enough Western aid. "We understand they may have problems meeting their commitments, but to allow them to decide unilaterally to break the agreement would be deadly from an environmental point of view," Claussen said.