PEKING, July 31, Reuter - The Soviet Union is willing to accept China's position on a long-standing dispute over the demarcation of their border along the rivers of northeast Asia, East European diplomats said today.

They said a speech by Soviet leader Mikhail Gorbachev on Monday in the Soviet Far East city of Vladivostok marked a crucial shift in Moscow's position on the border river issue, which led to serious fighting in March, 1969.

Gorbachev in his speech said, "The official border might pass along the main ship channel."

Moscow had insisted the border ran along the Chinese bank of the Amur (Heilongjiang) and Ussuri rivers, marking the boundary of the far northeastern spur of Chinese territory.

The Chinese have always held to the "Thalweg Principle" under which borders are judged to run along the deepest part of the main channel of a river, the principle that Gorbachev also now seems ready to accept.

In his speech, Gorbachev only referred by name to the Amur River, but the diplomats said they believed his comments also applied to the Ussuri River, site of Chenbao Island (Damansky Island) where the 1969 clashes took place.

The new Soviet position on the border river question, if accepted by China, would mean that Moscow had relinquished its claim to Chenbao Island, which lies on the Chinese side of the main channel of the Ussuri River, the diplomats said.

The island, about 100 metres (yards) from the Chinese bank and about 400 metres (yards) from the Soviet bank, has been under Chinese control since the 1969 clashes when Chinese forces repulsed a Soviet attempt to occupy the island.

The Chinese Foreign Ministry has not yet made any comment on the sections of Gorbachev's speech concerning Sino-Soviet relations, but one senior Chinese official said the speech was being studied carefully.

Asked if the new Soviet concession met the Chinese position on the border river question, one East European diplomat said:

"It matches the Chinese position as expressed in border talks with the Soviet Union in the 1960s and 1970s. But no talks on this subject have been held since the late 1970s."

The Sino-Soviet border was the scene of frequent incidents and clashes in the 1960s and early 1970s.

From 1966 to 1977, the Soviet Union refused to allow Chinese ships to sail through the main channel of the Amur River past the Soviet city of Khabarosk on the grounds that the river was a Soviet inland waterway.

Western diplomats have said Gorbachev's Vladivostok speech indicated a new willingness on the part of the Soviet Union to search for a compromise to end the 25-year-old split between Moscow and Peking.