China has sent three economic experts on an unofficial visit to the Soviet Union in the first such move in nearly two decades. Political observers interpreted the visit as the latest sign that tensions may be easing between the two communist giants.

Chinese sources said the three specialists arrived here 10 days ago as guests of China's ambassador to Moscow, Yang Shouzheng, and are expected to return to Peking later this week. The sources said the three were here to discuss various economic issues, including "Soviet management methods," with Soviet officials and experts.

The three men, whose names were not disclosed, have been received by Alexander Bachurin, deputy chief of the Soviet state planning committee.

The Chinese move followed a public call last month by Soviet Premier Nikolai Tikhonov for the resumption of a Sino-Soviet dialogue. In what appeared to be one of the most positive signals of a thaw in recent years, Tikhonov asserted that there were "no problems" between the two countries that could not be resolved "on the basis of equality and in the spirit of mutual understanding."

Diplomatic observers here said the unpublicized visit by the three experts could reflect Peking's current dissatisfaction with President Reagan's foreign policy. They specifically mentioned the Reagan administration's attitude toward Taiwan and the prospect of sales of U.S. weapons to the Taiwanese as factors in China's disenchantment.

The visit by the three Chinese, who are described as specialists on the staffs of two Peking institutes, is without precedent, according to political observers here.

Since the outbreak of the Sino-Soviet feud in the early 1960s, there have been no informal visits here by the Chinese. Apart from maintaining their respective diplomatic missions, the two sides have met annually to set up their trade list. Actual trade has been small for neighbors the size of China and the Soviet Union-- about $400 million in total volume in 1980.

Following the outbreak of border hostilities in 1969, the two sides opened negotiations, but these were broken off more than three years ago.

Moscow proposed last October that the two countries open talks aimed at improving relations or at the least resume border negotiations. Tikhonov publicly renewed the offer last month.

While the talks were not expected to remove bitter resentments accumulated over the past two decades, the Soviets apparently expect that any easing of tension could negatively influence Chinese relations with the United States.

The Sino-American rapprochement--particularly the opening of diplomatic relations in 1979 and subsequent cooperation--is viewed here as the principal threat to the Soviet Union in Asia.

Besides the Soviet overtures, there have been other indications here that Sino-Soviet relations have thawed slightly in recent months. Chinese sources said a Soviet official described as the head of an institute on foreign policy under the Soviet Ministry of Foreign Affairs visited Peking in January. He is said to have talked with Chinese foreign ministry officials.

There have been unconfirmed rumors here that Moscow and Peking plan to reopen border talks in the near future. Also, the Soviet press in recent months has noticeably scaled down its anti-Chinese rhetoric.