President Carter told a Chinese emissary in the Oval Office last Sept. 19 that the United States intends to continue supplying arms to Taiwan indefinitely as a contribution to Asian stability and to forestall developments that would be undesirable from the viewpoint of both big powers.

Carter did not spell out the obvious danger of a future Moscow-Taiwan military relationship in his talk with Chai Tse-min, newly arrived chief of the Chinese Liaison Office, according to informed U.S. officials. But there was little doubt among these officials that Carter's point was understood by the Chinese.

The president's justification for continuing U.S. arms sales to Taiwan, one of the most delicate and difficult issues in almost six months of secret negotiations with Peking, was disclosed yesterday as Carter administration officials described how the normalization of deplomatic relations with China evolved and where it may lead.

Among the other of developments, in a day of briefings and explanations of the dramatic announcement made Friday night, U.S. time, both here and in Peking, were these:

A senior Defense Department official told reporters that military analysts do not believe China could invade Taiwan successfully for at least five years, and that the analysts do not believe China has any intentin of launching such an invasion.

Treasury Secretary Michael Blumenthal and Commerce Secretary Juanita Kreps began making plans to go to Peking early next year for talks about expanded trade relations and the settlement of financial claims pending since the Communist takeovers of China in 1949.

Sen. Bob Dole (R-Kansas), charging that the Carter administration "caved in" to Chinese demands, called for early hearings by the Senate Foreign Relations Committee on future U.S. relations with Taiwan.

A senior administration official, briefing White House reporters said the United States still hopes that Soviet leader Leonid Brezhnev will come to Washington to sign a completed SALT treaty in mid-January, before the Jan. 29 visit here of Chinese Vice Premier Teng Hsiao-ping.

Most attention in Washington yesterday centered on the arrangements affecting Taiwan, the most politically sensitive part of the newly announced accord both here and in Peking.

Officials explained that the U.S. objective was to achieve the substance of Chinese peaceful intent regarding Taiwan and to enhance U.S. confidence in a peaceful settlement there, even though an explicit Chinese statement of peaceful intentions was considered unobtainable. Officially, China firmly regards the future reunification of Taiwan with the mainland as "an internal matter."

The United States acceded to the three basic Chinese conditions: sever diplomatic relations with Taiwan, withdraw all U.S. military forces, cancel all existing treaties. Nonetheless, in the administration view, the lengthy and highly secret negotiations produced three accomplishments regarding Taiwan's future.

First the United States insisted successfully that the Mutual Defense Treaty with Taiwan will be terminated with one year's notice as provided in the document rather than scrapped overnight. The effect of this, officials pointed out, is that the United States will have both a defense pact with Taiwan and diplomatic relations with Peking for a year from Jan. 1, 1979, when a formal treaty termination notice is to be given Taiwan and relations established with the mainland.

Second, the United States insisted on stating that it "continues to have an interest in the peaceful resolution of the Taiwan issue and expects that the Taiwan issue will be settled peacefully by the Chinese themselves.' Another part of this arrangement is that the Chinese would not make any statement contradicting the U.S. stand.

Third and perhaps most difficult, the United States insisted on continuing the sale of arms to Taiwan even after normalization of relations with Peking and termination of the military pact with Taiwan.

The eventual solution, in this case, was a carefully crafted set of statements at a White House briefing Friday night and by Chinese Communist Party Chairman Hua Kuo-feng in an unprecedented news conference in Peking. The Americans announced that the sale of "defensive arms" to Taiwan on a "restrained" basis will continue. Hua announced that "we can absolutely not agree to this," but that, nevertheess, normalization of relations with Washington will go forward.

Officials characterized as "inaccurate" a widely quoted UPI report last June 13 describing U.S. conditions for normalization as descrihed by Carter and other top officials to an off-the-record session of the Trilateral Commission. One of those conditions, as quoted at the time by UPI, was that China "must make clear, through a formula yet to be agreed upon, that it would not use force in seeking to reunite Taiwan to the Chinese mainland."

As described by official sources, Carter's bid for normalization of relations with Peking began in February 1977, when he informed the then chief of the Chinese liaison office here, Huang Chen, that he wished to move toward noraml relations. No timetable or detailed conditions are reported.

Secretary of State Cyrus R. Vance's trip to Peking in August 1977 was an attempt to explore a commonly agreed formula for solution of the Taiwan question. Administration officials said the Chinese were disappointed by the "exploratory" approach because they had reason to expect that the United States was prepared to move rapidly, based on the statements of previous presidents.

According to Carter administration officials, President Nixon in unpublished conversations with then Chairman Mao Tse tung and Premier Chou En-lai said it was his "hope" and "intention" to normalize relations at the end of his second term, by 1976. One official said there are suggestions that Nixon intended this as a Bicentennial spectacular as he left office. His term, of course, was cut short by Watergate.

President Ford, according to the official accounts yesterday, secretly told Chinese leaders that he hoped to be able to normalize relations early in 1977 if he was elected. The officials said that Ford was careful to add that this would depend on the arrangements to be worked out on the Taiwan issue.

In view of this history and other considerations, said a Carter administration official, "we did not have the option of temporizing. . . . we had the choice of moving forward or allowing the situation with China to erode."

The basic decision to go forward was taken shortly before the Peking journey of presidential assistant Zbigniew Brzezinski in May of this year, according to this account. Brzeziaski was authorized to say publicly, as he did at a state banquet, that Carter had "made up his mind" to normalize relations. He was also permitted to say secretly that Leonard Woodcock, the U.S. liaison chief in Peking, would be ready to begin negotiations on the question in a month.

Woodcock's negotiations with Chinese Foreign Minister Huang Hua actually began in early July, and involved six meetings between then and Dec. 4. Woodcock's instructions were drafted by a "China team" of four people, designated by written presidential order and enjoined to secrecy: Vance, Brzezinski, Assistant Secretary of State Richard Holbrooke and NSC China specialist Michel Oksenberg. Each instruction was personally approved by Carter.

A landmark event was the Sept. 19, White House meeting with Chai, the newly arrived head of the Chinese liaision office here. Carter outlined in detall U.S. terms for normalization as well as an overall international rationale for moving ahead.

Shortly after the session, as a sign of U.S. seriousness of purpose, Woodcock was instructed to notify the Chinese that Washington suggested Jan 1, 1979, as the date for normalization if details could he worked out.

In Washington, to assist the process and encourage Peking, Brzezinski met about 10 times since June with Chinese emissaries at his office, his home or the Chinese Liaison Office on Connecticut Avenuel.

A breakthrough on the Chinese side was a Peking meeting Dec. 4 at which Woodcock was given a "draft communique" for normalization by Chinese Deputy Foreign Minister Han Nien-lung. For the first time, China stated that its target date for normalization was also Jan. 1. And at the end of the meeting, Han told Woodcock that Vice Premier Teng Hsaio-ping, the most important leader, "will see you soon."

U.S. officials immediately sensed that is fundamental decision had been mad within the Chinese leadership to move ahead rapidly. Carter's China team waited expectantly for the Teng meeting. When nothing happened in a week, by Monday, Dec. 11, Brzezinski was authorized to call in the liaison office's Chai to prod the negotiations.

Brzezinski told the Chinese diplomat that Woodcock had been given his instructions, and expressed hope that they would be given speedy and serious attention. It was time to speak in political terms, not formalistic ones, Brzezinski said. And as an added incentive, he said that if normalization could be arranged by Jan. 1, top Chinese leaders would be invited to Washington early in the new year.

Within 12 hours, Woodcock had been ushered into the promised meeting with Teng. On Wednesday morning, Dec. 13, his report was in the White House, and Brzezinski could tell Carter that things were rolling.

Late that afternoon and unitl 1 a.m. the following day, Brzezinski, Deputy Secretary of State Warren Christopher (in the absence of Vance, who was in the Middle East), Holbrooke and Oksenberg drafted the proposed communique and other documents to be used and issued.Carter came back from an address to the Business Council after 9 pm., changed into jeans and joined the group until about 11 p.m.

Thursday about 1 p.m. the word came back from Woodcock of Teng's reaction, based on another meeting with the Chinese leader. Brzezinski took the cable to the Oval Office and told Carter, "I think you have it."

Final negotiation continued between Woodcock and Teng in Peking, and Brzezinski and Chai in Washington, until a few hours before the announcement. Meanwhile, Vice President Mondale, media adviser Gerald Rafshoon, political assistant Hamilton Jordan, legislative aide Frank Moore and a few other key people were brought abreast of the situation to plan the big announcement to be made Friday night.

By this account, the crucial U.S. decision was taken Sept. 19, two days after the euphoric end of the Egypt-Israeli summit meeting with Carter at Camp David. By historical accident or otherwise, the final announcement of U.S.-China ties would be made Dec. 15, two days before the end of the announced deadline for completion of the Egyptian-Israeli peace treaty. That deadline will pass without results, and with no success in sight, but the achievement of relations with China will take public attention away from the setback in the Middle East.