China warned the United States today against any further American concessions to Taiwan whether by the Carter adminstration or its possible Republican successor -- particularly arms sales.

U.S. Ambassador Leonard Woodcock was summoned to the Foreign Ministry to receive a formal protest against the Oct. 2 agreement under which "unofficial" delegations exchanged by the United Staes and Taiwan would receive full diplomatic privileges.

Official Chinese sources later added an unusually stern warning at a briefing for American correspondents here. U.S. arms sales, they said, tended to make the Nationalist government "cocky" and that might force Peking to seek other than peaceful means to resolve the reunification issue.

This tough diplomatic talk came only a day after the Chinese city of Canton declared null and void its six-month-old "sister city" agreement with Los Angeles because the city council there voted to fly the Republic of China flag on Oct. 10, the Taiwanese national day.

The sources emphasized China had no bias toward one political party or the other in the U.S. presidential elections since, they said, there were wise people in both who understood the overall strategic importance of strong Sino-American relations in the face of Soviet expansionism.

Some observers were surprised at both the timing and the vehemence of the Chinese reaction since the diplomatic privilege agreement was nearly two weeks old and had already been dealt with at length in the Chinese press.

Subsequently the State Department had denied the extension of privileges like diplomatic immunity to arrest and taxation constituted restoration of official relations, as the Chinese alleged.

One theory was that Peking had been sharply disturbed by the jubilant use made of the agreement by the Nationalist regime on Taiwan.