The mission to Peking of Assistant Secretary of State John H. Holdridge was "useful and a success," the State Department said yesterday, suggesting that continuing disagreement over arms for Taiwan is not likely to bring Sino-American relations to a new crisis point at this time.

Holdridge was scheduled to leave the People's Republic of China last night for a brief stopover in Japan before returning from three days of meetings centering on President Reagan's decisions on Taiwan arms sales.

The U.S. official brought the news that Reagan would not sell Taiwan new-generation FX fighter planes, but instead would continue sales of warplanes already in the Taiwan inventory.

The Mainland Chinese previously threatened to downgrade Sino-American relations if the sophisticated plane were provided. Following the announcement of the new decisions Monday, they issued a "strong protest" to continuing U.S. military sales to Taiwan.

State Department officials said the "positive and productive" discussions begun by Holdridge will continue in diplomatic channels in both Peking and Washington, indicating a continuing effort to reach an accommodation on the issue.

A permanent solution seems out of the question, since China objects as a matter of principle to the arming of Taiwan, and the United States is committed by both foreign policy and law to meeting Taiwan's defense needs on a continuing basis.

During the discussions in Peking, Holdridge and other members of his party dealt primarily with a Chinese team headed by Vice Foreign Minister Zhang Wenjin. Yesterday, the last day of his talks, Holdridge met with Vice Premier Ji Pengfei for about an hour.

Among the members of the U.S. team whose names were disclosed yesterday was John R. Davis, chief of the Eastern European office of the State Department. His presence indicated a considerable amount of attention in the talks to the current situation in Poland.

Peking has had little to say about the martial law crackdown in Poland. State Department officials have told members of Congress that the need to forge a united anti-Soviet front, including China, in light of the Polish situation accelerated the U.S. decision making on Taiwan arms.

The State Department denied, however, that any "quid pro quo" involving Poland was at stake in the arms decisions.