The Soviet Union and China have agree to open political talks in September in their first attempt in 10 years to formally regulate a wide range of bilateral issues.

With yesterday's announcement, both sides are apparently seeking a formal way to keep strained relations under control without their 30-year treaty of friendship, cooperation and mutual assistance, which expired in April.

Desptie China's announcement, the convening of negotiations may become complicated if Moscow refuses to hand back a Chinese citizen held in the Soviet Union.

China charged Tuesday that the Soviets staged a border incident by ambushing two Chinese civilians inspecting pastures on the Chinese side of the border. It added one man was killed and the other wounded, then both were dragged to Soviet territory. Moscow responded by asserting that the two were part of a four-man team of Chinese security guards that entered Soviet territory.

Moscow and Peking have conducted low-level talks annually on trade, river navigation and railway transportation, but the last political talks were held in 1969 when Soviet Premier Alexei Kosygin met with Premier Chou En-lai in Peking following a series of bloody border clashes.

Analysts here said that given the depth of Sino-Soviet ideological differences, the talks were not expected to lead to rapprochement. But they said that both sides may agree on a statement of principles that would take the place of the expired treaty.

A Chinese government spokesman in Peking announced yesterday that the talks would open in Moscow in mid-September and that the Chinese delegation would be led by Wang Yuping. He was China's ambassador to Moscow until his recent appointment as deputy foreign minister.

Diplomatic sources said affirmative Soviet reply to Peking's proposal to open talks was handed to the Chinese on Monday, although no Soviet announcement was made publicly. It was expected that the Soviet delegation would be led by veteran diplomat Leonid Ilyichev, who is deputy foreign minister.

Following the Kosygin-Chou meeting 1969, the two countries agreed to open negotiations on border traffic and possible minor adjustments to the border. But the Soviets have since consistently refused to discuss territorial questions with the Chinese, who contend that Moscow acquired thousands of square miles of Chinese territory under "unequal treaties" forced on Chinese emperors in the 19th century.

The border negotiations failed to produce results and were apparently discontinued in May 1978.

Apart from border problems, the forthcoming talks are expected to deal with the massive Soviet military presence along the Sino-Soviet frontier. China would like to see this presence reduced and the forces deployed further from possible conflict areas.

During the coming talks the Soviets are likely to emphasize such subjects as principles of relations, or a mutually honored code of conduct that could scale down tensions between the two Communist giants.

Analysts here noted, however, that while both sides have agreed to open political talks, they have not announced an agreement on the agenda. That, the analysts predicted, would be the first stumbling block.