Poland's ambassador to the United States, Romuald Spasowski, attacking the military crackdown in his homeland as a "cruel night of darkness and silence," was granted asylum in this country yesterday.

"A state of war has been imposed upon Poland, a state of war against the Polish people . . . . I cannot be silent," Spasowski said in a statement that he read to reporters at the State Department, four hours after it was disclosed that President Reagan had granted asylum to the ambassador and his family.

Spasowski, 61, the senior member of the Polish diplomatic service, spoke in heavily accented, but fluent English. With his wife behind him, wringing her hands, and a large number of security agents watching warily from the sidelines, the tall, goateed diplomat made little effort to disguise the emotion and strain in his voice.

"I cannot have any association, not speaking about representation, with the authorities responsible for this brutality and inhumanity," he said of the martial law in Poland. "I have decided this the moment I have learned that Lech Walesa, the most beloved leader of Solidarity, is arrested and kept by force.

"This, what I am doing now, is my expression of solidarity with him. I have decided to make this statement, to stand up openly and to say that I will do everything possible to assist the Polish people in their hour of need."

Four hours before Spasowski spoke, Secretary of State Alexander M. Haig Jr., during an interview on "Face the Nation" (CBS, WDVM), first revealed that the ambassador had asked for asylum and that Reagan personally had granted the request and ordered that Spasowski, his wife, his daughter and son-in-law be given protection.

State Department sources said that Spasowski had asked for asylum in a telephone call Saturday afternoon to John D. Scanlon, deputy assistant secretary of state for European affairs, and that he was placed under protection later that day. The sources said the situation was kept a closely held secret among only a few senior officials in the State Department and administration until yesterday morning when the president formally acted on the asylum request.

Spasowski has been Poland's envoy to five countries, and his tour of duty here, which began in 1978, marked the second time he had been posted as ambassador in Washington.

At one point in his career, he was the deputy head of the Polish foreign ministry, and his denunciation of the government he had served for so long seemed likely to deal a severe blow to the effort of Polish authorities to portray the crackdown as a purely internal strike against counterrevolutionary forces.

In diplomatic circles, Spasowski was known as a courtly, old-school diplomat of moderate views who made little secret of his sympathy with Solidarity and its efforts to force reforms in Poland's communist system. In this, he is known to have been influenced heavily by his wife, Wanda, who is a deeply religious Roman Catholic. (The names of Spasowski's daughter and son-in-law were not known, but they were believed to be members of the faculty at American University.)

Before last weekend's crackdown in Poland, he had been ordered to return home at the end of January, and the expectation was that his government planned to retire him from the diplomatic service.

During the last week, as he made daily visits to the State Department, his distress at the events in Poland was evident to everyone who talked with him, and it became a matter of open speculation about whether he would continue to support the authorities there and go back.

The answer came yesterday when Spasowski stood before a crowd of reporters and whirring television cameras in the vast Loy Henderson Conference Room of the State Department and denounced the Polish military's "steps to extinguish every ember of freedom, trying to eliminate independently minded people."

In what appeared to be an oblique reference to the Soviet Union's influence over the takeover, he said: "This carefully orchestrated and directed crackdown is not an internal Polish issue. This is the most flagrant and brutal violation of human rights, which makes a mockery of the Polish signature put on the final act of the Helsinki accords."

That is a 1975 agreement signed by the heads of 35 nations, including the United States. Among other things, it calls for respecting the civil rights and liberties of people in signatory countries.

"The only solution to the tragedy is a political solution, by dialogue," he asserted. "Nobody can put in prison 36 million people and make them slaves in the center of Europe . . . . The road to peace is the only road."

He appealed to the American people: "Show your solidarity, show your support and humanitarian assistance to those who are in such need at this hour."

To Polish Americans, he said: "Let everybody know that in your hearts and minds, you are with the people of Warsaw, of Gdansk, Krakow and Poznan, with the heroic workers of the shipyards and with the brave miners of Silesia."

Then, addressing other Polish diplomats, Spasowski made this appeal: "Be Polish and true to yourselves . . . . Do whatever your conscience dictates to assist our brothers and sisters in Poland."

There were no signs, however, that other Polish diplomats, here or in other countries, intended to follow his example. The second-ranking member of the Polish mission here, Stanislaw Pawliszewski, also is understood to have been ordered home, and some sources said they believed he had been told to leave immediately.

A call to Pawliszewski's Chevy Chase apartment was answered by a woman who said she was his wife. She said her husband was in Washington but not at home and refused to answer questions.

Another member of the Polish diplomatic mission here, who asked not to be identified, said of Spasowski's action: "I am angry because it is a step against Poland . . . . I don't understand a government officer who leaves Poland. It's a betrayal. He is a traitor."

Radio Warsaw said in a broadcast that "the circumstances have not been fully explained and are being investigated. Romuald Spasowski has for some time suffered from periodic depression and in this connection has been recalled and asked to return to Poland."

Neighbors of the Polish embassy residence at 3101 Albemarle St. NW said yesterday they were unaware of any unusual activity there Saturday. One neighbor said, though, that four or five cars apparently belonging to the FBI or Secret Service were parked outside the residence between 3 p.m. and 8 p.m. Saturday and that several agents went in and out of the house, although the neighbor said he had not seen Spasowski during that time.

Officials declined to say where the Spasowskis were being taken, but the normal procedure would be for them to be secluded under guard in a "safe house" in the area, as long as there was concern for their safety.

In other developments in the Polish crisis, a U.S. delegation, headed by Lawrence S. Eagleburger, assistant secretary of state for European affairs, left for meetings with America's West European allies aimed at working out a coordinated strategy for dealing with the situation.

Haig, in his TV interview, reiterated past administration statements that a variety of diplomatic, economic and "security-related" measures were under consideration for possible use against Polish authorities and the Soviet Union. But he refused to spell out what these measures might entail. Similar positions were taken by Defense Secretary Caspar W. Weinberger and presidential counselor Edwin Meese III in separate television appearance.