The Reagan administration said emphatically yesterday that it has given no assurances to China that nuclear-armed U.S. warships will not participate in a proposed port call to Shanghai.

If China insists on such assurances, which were mentioned to reporters Wednesday in Peking by Communist Party leader Hu Yaobang, the long-expected port call will not take place, a State Department statement indicated.

The State Department, which usually treads carefully in comments bearing on U.S. relations with Peking, was unusually blunt in addressing the nuclear-ship issue. "No United States ship visits can take place anywhere in the world, except under this policy" of neither confirming nor denying the presence of nuclear weapons on U.S. vessels, spokesman Ed Djerejian said.

State Department sources said the U.S. position on the ships issue and U.S. policy was passed to the Chinese by Assistant Secretary of State Paul D. Wolfowitz in a meeting yesterday with Zhang Zai, acting chief of the Chinese Embassy.

The Chinese party leader's statement was met by surprise on the part of State Department officials. The remarks could lead to international complications because the U.S. policy is at the heart of a U.S. dispute with New Zealand, which has refused U.S. port calls. Hu's remarks came as he prepared to embark on a mission to Pacific nations that will take him to New Zealand next week.

Final arrangements for the proposed U.S. warship visit to Shanghai have not been completed, according to the Defense Department. It was learned from U.S. sources that the Chinese asked earlier that one of the U.S. warships calling at their ports be a Spruance-class destroyer, an up-to-date and powerfully armed vessel.