The top rank of the Reagan administration watched with suspense and issues words of warning yesterday as the Soviet Union, according to reports reaching Washington, mounted a growing show of force in and near Poland.

Secretary of State Alexander M. Haig Jr. and Secretary of Defense Caspar W. Weinberger, on separate television interview programs, expressed concern about the Soviet military activities taking place under the aegis of a previously announced Warsaw Pact command-and-staff exercise.

The exercise, Soyuz-81, was to have been completed last Wednesday, according to U.S. officials. But the military activity was steadily stepped up as the Polish Communist Party, government and labor unions approached a crucial weekend of decision-making.

Soviet and Warsaw Pact forces around and inside Poland have been placed on a high state of alert and are standing by in case of an order to move, according to intelligence reports. As part of this program, newly deployed communications units have tied in all the military commands in a large area of the western U.S.S.R., Poland, Czechoslovakia and East Germany, the reports said.

The State Department had said as late as Friday that no "large-scale ground force movements" had been seen around Poland, but such movements have begun to show up since then, according to official sources.

Haig, on "Meet the Press" (NBC, WRC), said, "The situation is still very, very tense. There are some good and also some continuing worrisome signs."

The positive element, he went on to say, was "some indication that the moderate elements in the political structure of Poland seem to be surviving well at the moment and maybe will continue to prevail."

The worrisome signs he detailed included growing frictions within the Polish political leadership, economic troubles and food shortages as well as military indications associated with the Soviet bloc maneuvers.

The former NATO commander said, as in the past, that Soviet military intervention is "neither imminent nor inevitable." But he also said Soviet forces are "at a heightened state of readiness, with communications in place, and with some indications of increased posturing" toward military action.

Some of the "sophisticated communications capabilities" have been put in place without the participation or knowledge of the Polish military forces, Haig said. He also said that "readiness measures" in the Baltic military region of the U.S.S.R, near the Soviet-Polish border, and in East Germany have been noted.

Weinberger, on "Issues and Answers" (ABC, WJLA), expressed "very considerable concern" about the continuation of the Soyuz-81 exercise, saying that "a maneuver of that kind provides a perfectly good cover, or springboard, if you like, for an invasion."

Both Cabinet officers said that Soviet military intervention or indirect Soviet action to suppress the Polish free union movement through the use of Polish forces would have grave consequences for East-West relations.

Asked if there would be "a U.S. military response in any way, shape or form" to a Soviet invasion, Weinberger replied that the planned responses "cover a broad spectrum of activity: political, economic, diplomatic."

The defense secretary said European foreign and defense ministers with whom he has talked agree that a Soviet military intervention "would end any possibility of any useful or effective kind of arms limitation or disarmament talks" between East and West.

Sen. Charles Perry (R-Ill.), chairman of the Senate Foreign Relations Committee, said on "Face the Nation" (CBS, WDVM) that a possible U.S. military, tilt toward the People's Republic of China "probably is the most meaningful and significant thing" that could result from a Soviet invasion.

Percy said this was an "ongoing project" and "option" of the Carter administration last December, at an earlier point of heightened concern about Soviet intervention. At that time, Percy said, the office of Zbigniew Brzezinski, then presidential national security affairs adviser, asked the Pentagon for "a list of lethal weapons and equipment that if force was used by the Soviet Union in Poland could be and possibly would be sold or provided" to China.

After Percy's remarks, Brezinski issued a one-sentence statement saying, "While I cannot deny or confirm what specific options were being developed, I can say I generally endorse what Sen. Percy said on this subject."