Secretary of State Alexander M. Haig Jr. said yesterday that the United States is closely watching two new developments in relations between the Soviet Union and Poland, and he warned that any Soviet intervention there would run into "the broadest and most detailed consensus" in the West on a strong response.

Haig declined to specify the consequences of direct or indirect Soviet intervention in Poland, other than to say they would be "grave and lasting." He said that "the bottom line of the consequences has been made very clear to the Soviet leadership."

In an interview last night on public television's "MacNeil-Lehrer Report" and a meeting with State Department correspondents earlier in the day, Haig reflected a U.S. government assessment that the situation in and around Poland is more tense than before the Soviet Communist Party congress three weeks ago.

One of the developments raising the level of U.S. concern is what Haig described as "a huge exercise . . . about to take place" involving Warsaw Pact military forces.

State Department sources said that air, naval and ground forces of the Soviet Union and its allies throughout Eastern Europe have been alerted to participate in a very extensive "training exercise," and that some activity has begun.

U.S. intelligence is watching for any sign that the two Soviet infantry divisions and Soviet air units stationed in Poland might use the maneuvers to intervene in the internal political situation there. As of now, officials said, there is no sign of such intervention.

If a military maneuver in a single area exceeds 25,000 troops, the host country is obligated to notify other nations in advance under the terms of the 1975 Helsinki agreement between East and West. The State Department said yesterday that no advance notification has been received in this case.

In addition to the maneuvers, which are an annual affair in Eastern Europe, Haig expressed concern at "a harder line" taken by the Soviet leadership with the Polish Communist Party and government in recent weeks.

It is this seemingly impatient and tough position, echoed by several Eastern European communist leaders, that is the principal source of rising concern among some U.S. officials.

In answer to reporters' questions, State Department spokesman William Dyess said U.S. concern about Poland, at this point, has not approached the high level of apprehension that was felt late last year.

Haig commented on Soviet policy toward Poland, Afghanistan and other areas in discussing the possibility of early Soviet-American talks. He said that he expects to have new discussions promptly with Soviet Ambassador Anatoliy F. Dobrynin, who is due back in Washington next week from the party congress in Moscow, but that higher-level talks on the foreign minister or summit level are not in sight.

While declining to establish formal "preconditions," Haig related the future of the Soviet-American dialogue to Soviet activity worldwide. Because of Moscow's actions, he charged, peace is at "a rather precarious level."

Haig made clear that total Soviet military withdrawal and neutrality in Afghanistan are goals of the United States, but he added that even "an understanding" about a Soviet withdrawal and manifestations of Soviet restraint elsewhere could improve Washington-Moscow relations.

Regarding Central America, Haig said that the flow of arms to insurgents in El Salvador has slowed, and there is "some evidence" that the guerrillas are running out of ammunition.

He also said, however, that he is "as concerned" over a military buildup in Nicaragua as he is about the arms flows to El Salvador's rebels. According to Haig, Nicaragua is building an army far larger that others in that area, 50,000 troops "with vast amounts of sophisticated military equipment."

Haig dealt in cautious fashion with Thursday's appeal to the press, by an official he identified as acting Assistant Secretary of State John A. Bushnell, to reduce the focus on U.S. activity in El Salvador. Haig portrayed the message as a call for balance in the reporting on various international trouble spots.