The Carter administration as part of its normalization arrangement with China has agreed to place a one-year moratorium on new U.S. weapons sales to Taiwan.

The temporary freeze was not disclosed in the statements and briefings that accompanied the announcement of normalization of relations with the People's Republic of China last Dec. 15. Some members of Congress expressed surprise and concern upon learning belatedly of the U.S. commitment.

Carter administration officials said that the failure to make the moratorium public was inavertent and some officials said they assumed it had been made known at the time of the normalization announcement. However the record of press briefings by high officials shows that while the language used about arms sales to Taiwan was consistent with a one-year freeze such an arrangement was never mentioned.

The moratorium on sales to Taiwan, according to officials, applies only to new presidential commitments during calendar 1979, the period during which the U.S.-Republic of China mutual defense treaty is being abrogated.

U.S. deliveries to Taiwan of already contracted-for warplane components, antiaircraft missiles, tanks and other war materiel are to continue this year and in the several years after termination of the defense treaty. The cost of U.S. weapons in the "pipeline" for delivery to Taiwan is estimated at $720 million.

Officials said the moratorium does not apply to presidential decisions last October to permit Taiwan to manufacture 48 F5E or F5F warplance using U.S. technology and components and to purchase 500 Maverick missiles and aiming devices known as laser designators. The total cost is reported to be about $185 million.

Taiwan had asked to buy more powerful and longer-range warplanes, including the F4, but the Carter administration agreed to permit only a continuation of the Taiwan production of the F5E or F5F, which are considered more defensive in capability. Pentagon sources said Taiwan has not yet told the United States wheter it wishes to proceed with the transaction approved last October.

Beyond 1979, the United States is committed to make available to Taiwan "arms of a defensive character... on a restrained basis." It is not yet clear whether the Carter administration will continue to negotiate with Taiwan this year on new arms sales to be formally approved after Jan. 1, 1980.

China stated offically that it did not agree to permit a continuation of U.S. weapons sales to Taiwan, but conceded, in effect, that it agreed to disgree with the United Sates on the question. Recently Chinese Vice Premier Teng Hsiao-ping was quoted by a group of visiting U.S. senators as saying that Taiwan could keep its arms and military forces as well as its autonomy after reunification with the mainland.

Taiwan has denounced Teng's statements as "propapanda" designed to lull the United States; the government of President Chiang Ching-kuo has continued to reject negotiated reunification with Peking. On Dec. 29 Taiwan's official news agency quoted a government statement saying that Taiwanese forces will launch an attack on the Chinese mainland at "an appropriate and advantageous time."

In a related development, Secretary of State Cyrus R. Vance told a news conference yesterday that "there will be no tilts, one way or the other" in Washington's dealings with Moscow and Peking, the rival giants of world communism.

"It is U.S. policy that we will treat the People's Republic of China and the Soviet Union in a balanced way," Vance said. He added that "this is an absolutely fundamental principle... that we must always keep in mind in managing our relationship with these two countries."