The fate of the World Summit on Sustainable Development, to be held in Johannesburg, South Africa, in August, could rest on a meeting that opened yesterday on the Indonesian island of Bali. The U.N.-sponsored meeting, which runs for two weeks, aims to smooth out differences among nations on how to achieve the twin and rather daunting goals of protecting the environment and eliminating poverty. The U.S. decided against sending any high-ranking officials to the talks, a move environmentalists say demonstrates a lack of commitment to sustainable development. In part because of U.S. obstructionism, environmentalists fear the Bali talks will not achieve anything of lasting significance. But Emil Salim, a former Indonesian environment minister who heads the U.N. committee paving the way for Johannesburg, played down such concerns: “I sense a mood of optimism, a sense of getting conclusions [at Bali] so that Johannesburg will be successful,” Salim said.