Twenty years ago, Jay M. Gould predicted that the movie industry would soon find its yearly attendance declining by half; he was right, and at that point the industry began paying close attention to the New York economist. Last week, Gould made the same prediction: Total box office receipts, he says, will drop from the current total of about $1 billion a year to less than $500 million within 10 years. Gould, head of Economic Information Systems, was commissioned to make a new survey last year by TeleCulture; in a report delivered to the Screen Actors Guild and the Academy of Motion Picture Arts and Sciences, he said that the era of the blockbuster motion picture is nearing an end. The problem, he claims, lies with film studios slow to adapt to new technologies and intent on feeding escapist film to the young audience while ignoring adult viewers. Total weekly film attendance is already only a fourth of the 90 million total reached in the late 1940s, but Gould says that within three years it will sink to the point where the film industry will make more money from television than from theaters, where producers will have no choice but to move into the pay TV, cable and home entertainment areas they currently skirt. "An era has come to an end because of inflation," said Gould. "Studio heads today have gambled larger and larger sums on fewer and fewer big pictures. The fortunes of every studio depend on less product than ever before. It's a game of Russian roulette."