China and the Soviet Union concluded a week of talks Friday that sealed preparations for next month's historic Sino-Soviet summit but failed to narrow differences on a settlement for occupied Cambodia, East-bloc diplomats in Beijing said. They said a compromise is expected on at least one of the two outstanding disputes on Cambodia during talks next week between China and Vietnam, whose troops have occupied Cambodia since 1978. The diplomats, who asked not to be identified, said finishing touches were put on preparations for the May 15-18 visit by Soviet leader Mikhail Gorbachev, including work on a joint public statement. Gorbachev will meet with Deng Xiaoping and other Chinese leaders for the first Sino-Soviet summit since 1959.