The Reagan administration has told members of Congress that it had to make a quick decision last week regarding warplanes for Taiwan because the Polish situation required a united front, including the People's Republic of China, against the Soviet Union.

This administration rationale was supplied by State Department officials to explain the lack of full-scale congressional consultations. Only a few members of Congress were consulted before President Reagan's decision last Sunday that sophisticated F5G fighter planes would not be supplied to Taiwan.

Chairman Charles H. Percy (R-Ill.) of the Senate Foreign Relations Committee informed committee members in a confidential memorandum Dec. 15 that "we have a commitment from the State Department that it will consult the committee before a final presidential decision on arms sales to Taiwan." An aide to Percy said that "we expected a more formal consultation" than the few contacts that took place.

Percy, who was traveling in the Sudan at the time, was consulted by cable last Thursday, the day that a National Security Council meeting chaired by Reagan considered the Taiwan sales issue. The senator replied by cable Friday with some suggestions, according to his aide, who asked not be quoted by name.

Senate Republican Leader Howard H. Baker Jr. (Tenn.), who is a member of the committee, was contacted by cable while traveling in Latin America, sources said.

Percy's report to the committee last month arose from objections by Secretary of State Alexander M. Haig Jr. to scheduled testimony on the Taiwan arms issue in closed committee session by Assistant Secretary of State John H. Holdridge. Haig reportedly told the senators the subject was too sensitive to be discussed even in closed session.

In response to Haig's pleas, and after the assurance of consultation prior to the decision, Percy settled for an informal briefing by Holdridge of himself and two other senators, S. I. Hayakawa (R-Calif.) and John Glenn (D-Ohio).

According to congressional sources, the State Department this week stressed the importance of a solid international bloc, including China, to oppose the Soviet Union's involvement in martial law in Poland. State officials reportedly said that China was increasingly upset over the possibility of a high-profile sale to Taiwan, and that a speedy U.S. decision was considered important to avert a damaging falling-out with Peking.

Because the United States decided to replenish Taiwan's existing warplane inventory, China has condemned Reagan's decision instead of praising it. Administration officials said it is still unclear whether China will content itself with pro forma objections or, instead, push the disagreement to renewed crisis.