President Reagan and Secretary of State Alexander M. Haig Jr. have decided to make no change now in U.S. relationships with Taiwan and the People's Republic of China, but the delicate choices involved remain under active review, informed sources said this week.

The sources, while reporting that a top-level discussion of this subject took place last week between Reagan and Haig, said no definitive decisions were made on future implementation of the 1979 Taiwan Relation Act governing Washington-Taipei relations.

These source described last week's decisions as interim ones, pending a broader review and denied that there had been a major showdown on China policy between Haig and national security affairs advisor Richard V. Allen, as reported by CBS News.

During the presidentail campaign, Reagan at times advocated restoration of "official" relations between the United States and Taiwan. This stand brought strenuous public protests from Peking. In order to restore diplomatic relations with China, the Carter administration agreed to place US. relations with Taiwan on a nonofficial basis.

Reagan issued his most complete statement on the subject last Aug. 25, after the Taiwan issue had ballooned into a headlined controversy. In the statement, he accepted the Taiwan Relations Act as passed by Congress but was sharply critical of the Carter administration's implementation of it as "inappropriate and demeaning to our Chinese friends on Taiwan."

Despite Reagan's words, the changes in implementation he suggested last August have not been made. These changes include meetings between U.S. and Taiwan representatives in official offices, such as the State Department or the Foreign Ministry in Taipei, permission for Taiwan to open more quasi-foreign branches in this country, and resumption of training of Taiwanese military officers in the United States.

The decision last week, according to the sources, was to postpone any such changes pending a large policy review regarding relation with the People's Republic of China and Taiwan. However, the sources said such changes have not been ruled out for the future.

A senior official of Taiwan's Coordination Council for North American Affairs, which serves as the unofficial Taiwanese embassy here, said he is not impatient at the absence of immediate change in the "unrealistic and impractical arrangements" of the past administration.

The official said there has been a relationship of "mutual cooperation" with the new administration in its early weeks and suggested that changes are expected eventually.

According to administration sources, Reagan sent a personal message to Peking in his early days in office that he would abide by the Sino-American communique that was the basis for establishment of diplomatic relations in the Carter administration, even though he opposed it at the time.

The communique is subject to various interpretations. Peking, for example, has charged that provisions of the Taiwan Relations Act violate the terms, while Washington has insisted that they do not.

The source also said there has been no decision on the U.S. response to Taiwan's desire to purchase an improved U.S. jet fighter. No action is expected on this touchy issue in the immediate future, they said.