Describing the situation in Poland as "very dangerous, very bad," Secretary of State Alexander M. Haig Jr. voiced great concern yesterday that Poland is heading into a "critical weekend" that may determine whether the grim confrontation between labor unions and communist authorities will be settled peacefully or by force.

Though the Soviet Union and other Warsaw Pact allies have prolonged the military exercises under way in and around Poland, Haig suggested it is not Soviet military intervention that seems the most likely first step if force is employed. Rather, he pointed to a strong White House statement issued late Thursday that called attention first to possible internal suppression of the unions by Polish authorities.

"I would anticipate that," Haig said when questioned by reporters at a breakfast meeting yesterday. Other sources said yesterday that, beyond the outward signs of tension in the country, new intelligence information also has increased concern here about a possible internal crackdown.

While senior officials throughout the Reagan administration clung to their previous assessments that Soviet intervention was still not inevitable or imminent, one pointed out that "if there is a major crackdown internally [by Polish authorities], I think there will be fighting and, if there is fighting, you know what comes next," meaning Soviet reinforcements.

What role the Polish army might play, even in an internal crackdown, is anybody's guess, one senior official said. "I don't think anybody knows if they would resist or join. It might be mixed, because what they are talking about involves firing on or suppression of their own people," he said.

Haig said the Polish economic situation "is very, very serious. In fact, it's grave." As tensions sweep the country and food shops are bought out by worried citizens, Haig explained, the possibility of food riots " is a real thing . . . a contributor to the tensions . . . and tempers . . . that exist throughout the country."

Haig talked of "a very major split between hardliners and softliners" in the Polish communist hierarchy, and other officials here said that a showdown between those two factions may come at a meeting of the party's central committee on Sunday in Warsaw. If the hardliners win and demand that a state of emergency or martial law be declared and be ratified at a session of parliament set for Monday, then a nationwide workers' strike set for Tuesday could touch off what one U.S. official called "a civil war."

Haig and other officials spoke of an accumulation of tensions, including the four-hour warning strike that was carried out yesterday in protest against earlier beatings of union officials in Bydgoszcz. They believe the situation is even more dangerous than last December, when the Carter administration thought a Soviet invasion might be imminent.

U.S. officials said indications that recent secret votes in the parliament have gone against the softliners, including party chairman Stanislaw Kania, were additional signs that those wanting a crackdown may be winning control.Other officials said they believe hardliners staged the beatings in Bydgoszcz to bring tensions to a head and force a decision to crack down on the trade union leadership.

The West German government in messages this week to Washington, has already reportedly expressed a grim assessment of the situation in Poland, where Bonn traditionally has taken a less alarmist view than Washington. The Poles have requested emergency economic aid from West Germany and the United States. Haig said there are a number of possibilities for U.S. food aid, but officials said no decisions were likely until Poland's deputy prime minister, Mieczyslaw Jagielski, arrives in Washington next week.

The U.S. aid would be carried out in conjunction with other western countries but it would not be the kind of aid, officials said that would "bail the Soviets out" of their own troubles in Poland.

Defense Secretary Caspar W. Weinberger also spoke with reporters yesterday about the "pretty serious" situation in Poland. Weinberger said the Pentagon did not believe any organized Soviet units had actually entered Poland, beyond those previously stationed there, during the current exercises. But he said the fact that the exercises did not end Thursday, as the West expected, has added to concern here.

Weinberger said that the Soviets probably would rather not intervene militarily but that, if they do, one certain casualty would be the "effective end of any possibility" of talks with this country about the control of strategic or European-based nuclear arms."It would be absolutely futile to sit down with a country that behaves that way," Weinberger said.

Without knowing of Weinberger's remarks, a Soviet official interviewed yesterday said that U.S. threats to cut off relations with Moscow have little impact because there is nothing left of those relations anyway.

The official considered the situation between the two superpowers to be extremely dangerous, but said that threats of western sanctions over Poland strengthen the hardliners in Warsaw.

Poland, the Soviet official said, is in a catastrophic position, with no food, and he said the United States should end what he called the "foolish games" of encouraging the unions to deliver ultimatums to the Polish authorities.

The Soviet official claimed that the Reagan administration was using tensions in Poland, in Central America and with Moscow in order to sustain an expensive arms buildup in this country.

At one point in his meeting with reporters, Weinberger also said the Soviets were already above the allowed ceilings on nuclear weaponry allowed by the SALT II agreement signed between the two superpowers but never ratified here.

But later, when questioned further, he said he wanted to withdraw what he had said about the Soviets violating the Strategic Arms Limitation Treaty ceilings, a charge the United States has never made.

Finally, Weinberger said, "I don't know if the Soviets are exceeding the limits or not, but they are adding to their strategic strength."