China has rebuffed a new Soviet bid for improved relations by apparently insisting on major changes in the militant postures the two countries have adopted along the volatile Amur River border before substantive talks can begin.

The official Tass news agency disclosed the impasse yesterday. It said the Kremlin sent a telegram Feb. 24 seeking talks in either capital toward better relations but received negative reply from Peking on March 9. The Chinese, said Tass, "repeated unacceptable preliminary conditions it had advanced before."

Foreign sources here described these conditions as a series of Chinese demands "in relation to the territorial dispute between the two countries." These sources indicted that the Chinese have sought a package of changes in the status of troops and other aspects of the border dispute.

China and the Soviet Union have been feuding for years on ideological grounds that in part are rooted in historic, ethnic and territorial rivalries. The tension flared into a shooting war along the Amur River in the Soviet far east during the late 1960s and the Soviets since have nearly doubled their ground forces, according to Western estimates.

In recent weeks, the Chinese have called for the Soviets to make good on commitments dating from a 1969 visit to Peking by the Kremlin leadership, saying the Soviets must prove themselves by deeds, not words.

Tass, without describing the "preliminary conditions," said that China's meaning "is to sidestep discussion of the essence of the questions of improvement of interstate relations between the two countries and to continue its unfriendly course with regard to the Soviet Union . . . The latest session of the National People's Congress indicates that hostility to the Soviet Union continues to be elevated to the rank of state policy of China."

The Soviet message to the Chinese, as reported by Tass, seems certain to anger the Peking leadership. It referred to a joint statement that would have called for "mutual respect for sovereignity and territorial integrity." A phrase that has been used in the past to describe Soviet rejection of Chinese claims on land within Soviet borders.

The unsuccessful Soviet move comes at a time when the Chinese are making slow diplomatic headway toward better relations with the United States and Japan, two powerful nations mistrusted by the Russians. The fierce rivalry between China and the U.S.S.R. has been reflected in part in the recent border strife between Cambodia and Vietnam, with Peking backing the former and Moscow the latter.