President Carter, facing swelling congressional demands for an official statement of support for Taiwan's security, indicated yesterday he will veto any legislation that he considers in conflict with his administration's agreement to recognize China.

"I could not approve any legislation presented to me by Congress that would be contradictory or that would violate the agreements we have concluded with the People's Republic of China," the president said at a news conference.

The warning came amid increasing signs that Carter's failure to caution China about U.S. concern for Taiwan's comfort among members of Congress who support the general thrust of his China policy.

Yesterday, when the White House sent to Congress its proposal for a private corporation to handle future U.S. relations with Taiwan, Sen. Frank Church (D-Idaho) -- the man whom the administration has asked to sponsor the bill -- characterized it as "deficient and in need of improvement."

"The most glaring deficiency is the failure of the legislation to provide a statement of official U.S. policy concerning the future security of Taiwan," said Church, who is chairman of the Foreign Relations Committee.

"In recognizing the People's Republic of China, the president failed to obtain from the Peking government a commitment that mainland China will not attempt reunification with Taiwan by force of arms," Church added.

He said it is "crucial that the United States adopt a firm statement of policy, having the force of law, that U.S. recognition of China rests on the assumption that any resolution of the Taiwan question will be sought only by peaceful means.

"When the Foreign Relations Committee considers the Taiwan legislation," Church warned, "I will do all that I can to bring about committee approval of a strong statement of national policy to be incorporated in the legislation that will both send a signal to Peking and reassure the people of Taiwan."

The statement added Church's voice to the growing chorus of congressional moderates and liberals whose concern about the Taiwan question is threatening to create a rough passage for Carter's China policy when those elements of it requiring congressional approval reach Capitol Hill.

Earlier this week, Sen. John H. Glenn (D-Ohio), chairman of the subcommittee on East Asia, warned that peaceful settlement of the Taiwan issue must be "the immediate guiding principle" in U.S. dealings with China, and two of the Senate's most influential liberals -- Edward M. Kennedy (D-Mass.) and Alan Chanston (D-Calif.) -- introduced a resolution that would reaffirm U.S. concern for Taiwan.

The Kennedy-Dranston resolution, which states that the United States would consider an armed attack on Taiwan "a danger to the stability and peace of Asia," was intended as a counter to efforts by congressional conservatives to impose more restraint on Carter's China policy.

The aim of Kennedy and Cranston was to give members of Congress a chance to demonstrate their concern about Taiwan without at the same time voting for legislation that might undo the administration's agreements with Peking.

However, Carter indicated yesterday that he is unwilling to accept even the relatively soft language of the Kennedy-Cranston resolution. He said:

"It really don't believe that any resolution is needed. I think our legislative proposal and the announcement made about normalization -- the combination of those two -- is adequate."

Referrin to his decision to break diplomatic relations with Taiwan and recognize Peking as the government of China, Carter asserted, "I don't see this as an opening for bloodshed or war. I think the statements made by the Chinese leaders since the announcement of intentions to establish relations have been very constructive and have indicated a peaceful intent."

He characterized the impending visit here of Chinese Vice Premier Teng Hsiao-ping as an occasion that he hopes will provide "stability and peace not only in the western Pacific but in the entire world."

Meanwhile, Rep. Clement J. Zablocki (D-Wis.), chairman of the International Relations Committee, and 51 other House members called on Carter to raise with Teng the problem of continued Chinese nuclear tests that have caused radioactive fallout in the United States.

In a letter initiated by Rep. Jonathan B. Bingham (D-N.Y.), the lawmakers called the atmospheric tests "an act of aggression" and said normalization of relations cannot be satisfactory while contamination from the tests continues.

In the legislation sent to Congress yesterday, the administration calls for establishment of a Washington-based American Institute in Taiwan, which would have field offices there to handle trade, cultural and consular relations.

Washington, which broke diplomatic relations with Taiwan on Jan. 1, insists that future relations must be handled on a nonofficial, people-to-people basis. However, the Taiwan government has not agreed to this arrangement and mounted a vigorous lobbying and public relations campaign to retain some kind of governmental tie.

Administration sources said yesterday that negotiations with Taipei are continuing and added that they believe the Taiwanese eventually will accept the proposed arrangement.

The proposal calls for the institute to have an initial budget of about $2 million and be staffed by approximately 50 State Department officers, who would temporarily be separated from the government service. David Dean, a retired Foreign Service officer with extensive China experience, has been chosen as its director.

In other comments regarding foreign affairs, Carter said:

The United States and Soviet Union continue to make "steady progress" toward completion of new strategic arms limitation treaty (SALT). He said he has no doubt that the Soviets are negotiating in good faith, though he described them as "tough bargainers."

Shipment of U.S. fuel supplies to Iran does not constitute interference in that country's internal affairs. Carter would not comment on charges by a House committee that he and other policymakers contributed to an "intelligence failure" in Iran, on grounds that any comment could be unwise in view of the "sensitive situation" in Iran.

He does not believe the Teng visit will impair U.S.-Soviet relations.He said the United States will be cautious in keeping a balance in its relations with the two giants of world communism.