Peking today mounted sharp protests against continued U.S. arms sales to Taiwan and possible dicussion of the sale of intermediate fighter planes, what appeared to be the most severe public Chinese comment in a year on what generally have been steadily improving Sino-American relations.

"While declaring that it will do nothing to impede the process of rapprochement between the Chinese mainland and Twaian, the U.S. government actually keeps transporting huge quantities of arms to Taiwan," a commentator for the official New China News Agency said in a dispatch early today. "This discrepancy between words and deeds represents nothing but bad faith in international relations."

The Chinese protest follows by a week an unusual attack by the official Chinese press on Republican Party presidential candidate Ronald Reagan for his suggestions of stronger U.S. ties with Taiwan. A commentator in the official People's Daily said June 14 that "if the United States reestablished 'official relations' with Twaian according to the policy announced by Reagan, it would imply that the very priniciple which constitutes the foundation of the Sino-U.S. relationship would retrogress against the will of the two peoples."

The commentator applauded, however, the official U.S. government position against "turning the clock back," and seemed to suggest that the Reagan attack posed no real threat to the improving relatinship. "Friendship and growing cooperation between the two peoples are a historical trend which cannot be checked by a tiny adverse current in the development of the Sino-U.S. relationships," the June 14 commentary said.

Today's protest appeared to be sparked by reports, mentioned in an accompanying dispatch from the Chinese agency, that U.S. Sen. Richard Stone (D-Fla.) had disclosed a U.S. State Department decision to allow American companies to discuss sale of FX figherts to Taiwan.

[A spokesman in Stone's office said FX is a generic name for an intermediate fighter plane. Several American companies would present their versions of the FX to Taiwan negotiators, the spokesman said. Northrup's FX, for example, is called the F5G.]

The Chinese have never been happy about American arms sales to their Nationalist Chinese adversaries on the island, but have been particularly sensitive to any possibility of more advanced equipment reaching Taiwan.

"It is obvious that the continued and increased arms sales by the U.S. government to Taiwan constitute a breach of the principles embodied in the agreement on the establishment of diplomatic relations between China and the United States and are harmful to the development of Sino-U.S. relations in a normal way. The chinese people certainly could not remain indifferent towards such a U.S. move," the commentary said.

Today's commentary expressed direct concern for the future of Sino-American ties. It was particularly striking because at the time of the announcement early this year of renewed U.S. arms sales to taiwan, the official public Chinese reaction was nothing more than a vague sentence in the middle of a short dispatch noting that such sales contradicted the Chinese position.

When Washington and Peking agreed to normalized relations in late 1978, they also agreed to disagree over the arms question, but officials had expected a sharper response when the announcement of renewed sales was made earlier in the year. Apparently the Reagan remarks and the prospect of FX sales convinced Chinese policy-makers that a stronger response was now necessary.

The Chinese news agency noted that despite a U.S.-declared moratorium on arms sales to Taiwan in 1979, the United States did sell the Nationalists about $800 million worth of equipment during that period in the name of "honoring previous commitments." It lised in detail the new set of arms, valued at about $280 million, promised to Taiwan at the beginning of 1980, including I-Hawk anti-aircraft missiles, the Sea Chaparral ship anti-aircraft missile, the TOW anti-tank missile, a shipboard weapons fire control system with 76mm rapid-firing guns and improved electronic identification system.

The Chinese dispatch did not refer to American statements that Taiwan would only receive weapons of a "defensive" capacity which would not allow attack on the Chinese mainland. Long-range fighters like the F15 have been excluded from Taiwan sales for this reason, U.S. officials have said.

The Chinese just completed a high-level military delegation visit to the United States led by Vice Premier Geng Biao, and there are no indications as yet of any change in plans for further exchanges.