By Michael Martina and David Brunnstrom WASHINGTON (Reuters) – U.S. Ambassador to China Nicholas Burns said on Friday he had started talks with Beijing on renewing a landmark scientific cooperation agreement, and while the deal needed to be modernized, prospects for a new one were uncertain. Controversy over the renewal of the U.S.-China Science and Technology Agreement (STA) – the first accord between the two countries signed in 1979 after the official establishment of diplomatic ties – has grown amid U.S. accusations of China’s theft of U.S. scientific and commercial achievements. The U.S. S…