TENG HSIAO-PING'S four days in Washington were not quite the unalloyed triumph that the American managers of his tour seem to have anticipated. True, he proved himself the quick and jolly fellow of his press notices. He had lengthy talks with Jimmy Carter, and these may produce cooperation or at least understanding on matters of common concern, such as Korea. He signed various bilateral agreements and discussed others, all designed to flesh out the skeleton of diplomatic normalization.

On the critical Taiwan issue, Vice Premier Teng calmed some (though not all) congressional fears -- mostly by indicating that the People's Republic of China could live with some sort of explicit congressional assertion of the American interest in seeing the Taiwan question resolved peaceably. The administration had been noticeably skittish about Congress putting its fingerprints on China diplomacy. Mr. Teng seemed to take the prospect more in stride.

It was not apparent, however, at least from the Washington part of his tour, that Mr. Teng will succeed soon, if at all, in gaining massive loans for modernization. He has openly committed himself to raise the living standards of China's 900 million-plus people. It is a colossal economic task and, for him, a great political gamble, and it is not clear how any amount of good will can trigger a flow of resources on the scale essential for his ultimate success.

It was not apparent either how Mr. Teng evaluates the difference between his and Mr. Carter's basic international outlooks. Peking wants quite simply to put Washington in anti-Soviet harness -- perhaps even, at the moment, to have Washington stand by approvingly while China, which has 10 divisions at the ready, teaches Soviet-supported Vietnam a lesson for invading Cambodia. Washington's more complex purpose is to have Peking play a supporting role in the American effort to cooperate as well as to compete with the Kremlin.

In an interview published as he arrived and in some remarks here, Mr. Teng vented his conviction that the Russians are up to no good. Some administration figures sniffed that Mr. Teng was "interfering" in internal American affairs by encouraging opposition to SALT. Perhaps. But, if that's what Mr. Teng really thinks, we are better off for knowing it now. His candor underscored that the basis for Sino-American cooperation is broader than it was but not unlimited. Mr. Carter made the point with a host's obliqueness yesterday. He should find an early public opportunity to let the Chinese, and the Russians, and the American people, know more clearly just where he thinks the new Sino-American relationship is headed -- and just how far he wants to go.