Last month a high Chinese official said some awkward things about American naval vessels bearing nuclear arms. In response the United States last week postponed a projected visit of three destroyers to Shanghai.

The two actions seemed casual, almost lazy, like games played by swimmers under water. But in fact they announce a new and highly uncertain stage in the confused relations between Peking and the Reagan administration.

President Reagan came to office saying such kind things about Taiwan that the progress in Sino-American relations initiated by President Nixon, and consolidated by Presidents Ford and Carter, was jeopardized. China complained that Reagan's unlimited support gave the Republic of China, also known as Taiwan, no incentive to reach a political settlement with the People's Republic of China, a k a Communist China.

Those complaints were resolved on Aug. 17, 1982, when the United States and mainland China agreed that American military aid to Taiwan would slowly tail off, and eventually cease. On that basis, Peking rolled out the welcome mat to a series of American visitors. To each the Chinese expressed interest in acquiring American technology. But different officials rendered different answers.

Secretary of State George Shultz, who came in February 1983, seemed aloof to the Chinese. He combined skepticism about the effectiveness of the Chinese economy with doubts that Peking would stay apart from Moscow.

Caspar Weinberger, in September 1983, while more interested, refused a blank check on sales of sophisticated military equipment to a Communist country. But President Reagan, in March 1984, flashed a green light for technology transfer. In May, Secretary of Commerce Malcolm Baldrige announced in Peking an American policy facilitating technology transfers to China.

The next high-level visitor was Navy Secretary John Lehman. He went in August 1984, when everybody else was saluting the renomination of Reagan at the Republican Convention. Lehman, who is the most assertive of the service secretaries by far, arranged for sale of a package of naval equipment, including anti-submarine warfare (or ASW) weapons, and some gas-powered engines for destroyers. As a symbol of that deal, three American destroyers powered by the engine were scheduled to make a port call on Shanghai this month. The call would have been the first by a U.S. warship since China went communist in 1949.

But on April 10, China's Communist Party secretary, Hu Yaobang, told journalists from Australia and New Zealand that the American destroyers would not carry nuclear weapons. Next day, the State Department objected that it was against U.S. policy to say whether naval vessels were carrying nuclear arms. State asserted that any deviation from the policy would compromise naval ties with Japan, which had strict rules against calls by ships with nuclear arms. It was also pointed out that this country had broken defense relations with New Zealand, when Prime Minister David Lange insisted on assurances that a visiting U.S. destroyer not be carrying nuclear arms.

The Chinese did not yield. On the contrary, their embassy in Australia put out a statement that deliberately confused the issue of ships bearing nuclear arms with ships powered by nuclear engines. Behind- the-scenes negotiations convinced U.S. diplomats of a multiple muddle.

For one thing the Chinese are divided on the pace of internal economic reform. Hu Yaobang wants to conciliate the go-slow interests. His followers apparently line up with the party chief on all issues, even the destroyer visit, where he seems to have blundered.

Many Chinese are also gushing about the Gorbachev regime. Some at least fear a defense deal with the United States would compromise better ties with Moscow. Finally, the Chinese seem truly confused about what military equipment they really want.

Some Chinese officials talk about purchasing anti-tank weapons from the Army, others about buying air defense systems. Still others are just window-shopping.

But the United States also is uncertain. While the Navy got there fustest with the mostest, Taiwan and most other American friends in the Western Pacific point out there is a much better case for increasing Chinese anti-aircraft and anti-tank strength than for improving the Chinese navy. A recent study by the Heritage Foundation shows that a stronger Chinese navy can do little to contest the Soviet fleet in the Pacific. But it is bound to worry Taiwan and to sharpen existing territorial conflicts with the Philippines, Malaysia, Indonesia and Thailand.

The basic point is that the administration has yet to put together a strategy for China. Free swingers such as Lehman merely fill a vacuum left by the White House, the State Department and the top brass at the Pentagon. Worse still, the Chinese imagine that by drawing close to Moscow, Peking can squeeze more out of the United States. So the need of the moment is straight talk. All parties have a strong interest in not outsmarting themselves by overly clever political games.