"Two-time loser comes back" was the main theme of comment engendered by the return of Teng Hsiao-ping to a top leadership post in China last week. But in fact the personnel reshuffle in Peking portends a far wider policy change.

A kind of political interregnum under a caretaker government has come to an end. China has already embarked upon a new domestic progam, and seems about to launch a foreign policy that provides an opening for easier relations with Washington.

During the long period of Mao Tsetung's reign, No. 2 men came and went, bringing with them various changes in policy emphasis. The last administration under Mao's reign was headed by Premier Chou En-lai and lasted from roughly 1971 to Chou's death in 1976.

As premier, Chou subordinated revolutionary ideology and social transformation to the needs of economic modernization. In keeping with the modernization theme, he initiated the opening to the West that led to President Nixon's visit to Peking in 1972.

Chou's designated successor was Teng Hsiao-ping, a former party secretary disgraced during the Cultural Revolution but brought back in 1973 as first deputy prime minister. In the first months of 1976, Teng moved strongly to carry out Chou's mandate for modernization. But he ran athwart the revolutionary zeal of Mao's wife, Chiang Ching, and her three allies in the so-called Shanghai Group, which was later stigmatized as the Gang of Four. In April 1976 Teng was ousted in disgrace.

At that point there began an interregnum with a caretaker government under a then little-known leader, Hua Kuo-feng. The interregnum continued through the death of Mao in September - when Hua, who had become premier, also became party chairman - through the purge of the Gang of Four, and on to the slow rehabilitation of Teng himself. With Teng's reemergence as first deputy premier, and the expulsion of the Gang of Four from the party last week, the interregnum is over. A Teng administration has begun.

Already the domestic course of the new administration has been blocked out. In a series of conferences and directives. Teng has stressed all the themes of modernization he inherited from Chou. He is pushing for improved industrial management, science and technology, agricultural productivity, military modernization, education and foreign trade.

Typical of the Teng approach is his emphasis on the learning component of education as distinct from its ideological function. He has said that the purpose of schools is "the spreading of knowledge" and has warned against "insulting and humiliating professors."

Foreign policy is more ambiguous. For one thing, Teng was particularly tough when he met with Henry Kissinger prior to President Ford's China trip in 1975. For a second, Peking has recently made a series of moves - in trade, fisheries and navigation - that work to ease the most acute practical difficulties with the Soviet Union.

Still, the Washington readers of the Chinese tea leaves are basically optimistic. They discount Teng's performance with Kissinger on the grounds he was acting under pressure from Chiang Ching and her revolutionary colleagues. They see the moves toward Russia as bargaining steps designed to remind Washington that China can always turn to Moscow if necessary.

They believe that, at bottom, domestic considerations are pushing Teng to renew the opening to the West that Chou initiated. Teng's internal program, in their view, requires expertise, equipment and credit from Japan, Europe and, to a lesser extent, the United States. The United States is of prime importance to China during the modernization as a security guarantee against Russia. Indeed, Albania, that ultimate Communist maverick, has been turning against China precisely because Peking is tilting toward the West.

Against this background, the visit to the People's Republic by Secretary of State Vance next month holds a fair prospect. The Chinese are unlikely to demand that Washington abandon all connection with Taiwan before it seeks any further cooperation with Peking. On the contrary, there is hope that Vance can set the stage for forward motion in Sino-American relations on a wide range of secondary issues such as trade, credits and cultural exchange. Progress on these items can move steadily forward over several years until the day when American opinion is finally prepared for the break with Taiwan that must eventually come as the price for full normalization of relations with Peking. For all these reasons Secretary Vance, who met with Teng in a visit to China in 1975, is "pleased" at the prospect of seeing him again.