Two British warships begin a five-day visit to Shanghai on Friday, marking the first port call to China by a nuclear-capable navy since a visit by U.S. Navy ships was canceled more than a year ago over the sensitive issue of whether the ships would carry nuclear weapons.

In this case, the Chinese have declined to say whether they asked for assurances from the British that the ships would not carry nuclear arms. It appeared, however, that the Chinese had sought no such assurances as they did with the United States.

China instead restated its policy that it does not allow foreign military vessels armed with nuclear weapons to visit, and Britain repeated its policy of neither confirming nor denying whether its vessels are carrying nuclear arms, the same policy followed by the United States.

A western diplomat said the British port call -- there was an earlier one in 1980 -- could set a precedent for the U.S. Navy's first China visit, possibly next year.

The port calls are formally described as "good will" visits, but the British and American navies attach importance to them for symbolic reasons. The Americans also view port calls as a normal part of a developing U.S.-China defense relationship that has included some limited American arms sales to China and extensive visits by high-ranking defense officials and military officers.

China sent Yang Dezhi, Army chief of staff, on a visit to the United States earlier this year. On the U.S. side, the diplomat said that discussions are under way on a possible visit to China within six months by Caspar Weinberger, the U.S. secretary of defense, on his second such trip.

The British warships arriving in Shanghai on Friday are the destroyer Manchester and the corvette Amazon.

Neither Chinese nor British officials would say how the two sides had resolved the issue of China's policy of not allowing foreign military vessels armed with nuclear weapons to visit China.

The United States and China failed to reach final agreement on the anticipated U.S. Navy visit to Shanghai last year after Communist Party General Secretary Hu Yaobang said that U.S. ships would not be carrying nuclear weapons when they made the port call. Hu and a senior Foreign Ministry official said in an interview that the U.S. government had given assurances to this effect.

The State Department immediately denied that such assurances had been given or that the United States had changed its policy. The U.S. policy of refusing to confirm or deny whether U.S. ships carry nuclear weapons is designed to keep the Soviet Union guessing.

Hu Yaobang's comment was seen by some diplomats as a misstatement. But some Chinese officials reportedly were also unenthusiastic about a U.S. port visit when the Chinese were negotiating with the Soviets and attempting to project an independent foreign policy image.

It was difficult for the Chinese to back away from Hu's statement, but they seem to have found a formula in the case of the British by simply restating their position and not challenging the British position.