Arthur C. Clarke, a writer whose seamless blend of scientific expertise and poetic imagination helped usher in the space age, died early Wednesday in Colombo, Sri Lanka, where he had lived since 1956. He was 90. Rohan de Silva, an aide to Mr. Clarke, said the author died after experiencing breathing problems, The Associated Press reported. Mr. Clarke had post-polio syndrome for the last two decades and used a wheelchair.

From his detailed forecast of telecommunications satellites in 1945, more than a decade before the first orbital rocket flight, to his co-creation, with the director Stanley Kubrick, of the classic science fiction film 2001: A Space Odyssey, Mr. Clarke was both prophet and promoter of the idea that humanity's destiny lay beyond the confines of Earth.

Other early advocates of a space program argued that it would pay for itself by jump-starting new technology. Mr. Clarke set his sights higher. Paraphrasing William James, he suggested that exploring the solar system could serve as the "moral equivalent" of war, giving an outlet to energies that might otherwise lead to nuclear holocaust.

Mr. Clarke's influence on public attitudes toward space was acknowledged by American astronauts and Russian cosmonauts, by scientists like the astronomer Carl Sagan and by movie and television producers. Gene Roddenberry credited Mr. Clarke's writings with giving him courage to pursue his Star Trek project in the face of indifference, even ridicule, from television executives. In his later years, after settling in Ceylon (now Sri Lanka), Mr. Clarke continued to bask in worldwide acclaim as both a scientific sage and the pre-eminent science fiction writer of the 20th century. In 1998, he was knighted by Queen Elizabeth II. He played down his success in foretelling a globe-spanning network of communication satellites. "No one can predict the future," he always maintained.

But as a science fiction writer, he couldn't resist drawing up timelines for what he called "possible futures." Far from displaying uncanny prescience, these conjectures mainly demonstrated his lifelong, and often disappointed, optimism about the peaceful uses of technology - from his calculation in 1945 that atomic-fueled rockets could be no more than 20 years away to his conviction in 1999 that "clean, safe power" from "cold fusion" would be commercially available in the first years of the new millennium.

Mr. Clarke was well aware of the importance of his role as science spokesman to the general population: "Most technological achievements were preceded by people writing and imagining them," he noted. "I'm sure we would not have had men on the Moon," he added, if it had not been for H.G. Wells and Jules Verne. "I'm rather proud of the fact that I know several astronauts who became astronauts through reading my books."