The United States has agreed for the first time to supply arms to the People's Republic of China, Secretary of State Alexander M. Haig Jr. announced tonight after three days of wide-ranging talks with Chinese leaders.

Haig said the decision had been made in Washington to remove China from the munitions-control restrictions preventing any sale of lethal weapons to this Asian communist country, which in the 1960s was considered America's most implacable foe.

Chinese arms requests, once the restrictions are lifted, will be considered on "a case-by-case basis" after consultation with Congress and allies, according to Haig. There was no public indication here of the types of arms the Chinese might be interested in, but Haig noted that potential Chinese requests may be developed in a mission to Washington next month headed by Liu Huaqing, vice chief of the Chinese general staff.

The arms decision, taken in the context of what American and Chinese officials described here as growing coordination and cooperation against the Soviet Union, is likely to prompt a strong response from Moscow, China's arch-rival and neighbor.

The U.S. has been moving toward a close military relationship with China by slow degrees, especially since the visit here by then-defense secretary Harold Brown in January 1980, shortly after the Soviet invasion of Afghanistan. Until now, however, Washington's limit was the supply of technology with possible military application and "military support equipment" such as radar equipment trucks and transport aircraft.

The decision to tell the Chinese leaders that the United States is prepared to make them eligible to purchase arms was made by President Reagan shortly before Haig left Washington for Peking, according to U.S. sources.

Haig gave no indication of whether the administration is considering government financing or other military aid in connection with Chinese weapons purchases. There are currently barred by U.S. law. Haig did say that the Reagan administration intends to ask Congress to amend U.S. laws "which lump the People's Republic of China with the Soviet Bloc."

Apparently deferring to Chinese sensibilities, Haig stopped well short of describing the Washington-Peking relationship as an alliance. He said he informed Chinese leaders that the United States intends to treat China "as a friendly nation with which the United States is not allied but with which it shares many interests."

It was unclear tonight just how far Haig's talks had taken Sino-American collaboration in opposition to Soviet activities in Afghanistan, Cambodia and other areas. Chinese Foreign Minister Huang Hua said that "our two sides do not entirely share the same views" on international issues but that both sides stressed the need "to increase consultations and coordination between themselves, as well as with other countries while taking actions, with each proceeding from its own position."

Haig said the two sides resolved "to coordinate our independent policies in order to limit the Soviet Union's opportunities for exploiting its military power."

Asked at his news conference Tuesday whether the new U.S. decision on arms for China "has any connection in your mind with the events in Poland?" President Reagan replied, "No, I don't see any connection between China and what's going on in Poland." He added, "I think the Poland situation is going to be very tense for quite some time. . . ."

[In response to further questioning, Reagan said that any proposals about aid or weapons for China as a response to a Soviet invasion of Poland "might have been contingencies that were discussed. Certainly they are not policy in our administration."]

Haig's visit was preceded by Chinese criticism of Reagan's policy toward Taiwan, the former U.S. ally that Peking considers to be part of China. Even though the new president has yet to formalize his Taiwan policy, Peking in recent weeks has issued official statements criticizing hints that Washington is planning to sell new arms to the island government or upgrade U.S.-Taiwan relations. After three days of discussions, both sides indicated that they had aired their views but had failed to resolve what Chinese and American officials agree is the main sticking point in bilateral relations. Nevertheless, both parties seem willing to isolate the issue while they allow the overall relationship to flower.

High ranking Chinese officials said privately that although U.S. participants had tried to make a distinction between defensive and offensive weapons sold to the island, their Chinese counterparts had persisted in opposing all weapons sales to Taipei.

Haig, for his part, refused to discuss details of talks on the Taiwan arms-sales question, saying it is a "very sensitive issue" for the Chinese. He said he had explained to the Chinese that Washington intended to pursue the "unoffical relationship" Americans have enjoyed with "the people of Taiwan" since the United States broke diplomatic ties with Taipei in 1979 and normalized relations with the mainland.

This U.S. position "was understood" by the Chinese side, Haig said. But when he was asked whether his Chinese counterparts "accepted" the position, he demurred, saying, "the issue is best explained by the words, 'they understood.'"

An American official said that while no assurances were given about future American arms sales to Taiwan, the U.S. side made clear that "the United States won't do anything precipitously to exacerbate the issue."

[President Reagan said yesterday that the U.S. decision to authorize case-by-case arms sales to China does not represent a change in U.S. policy toward Taiwan. "I have not changed my feelings about Taiwan," he said. "We have . . . a law, called the Taiwan Relations Act, that provides for defensive equipment being sold to Taiwan as well as other things in the relationship and I intend to live up to the Taiwan Relations Act."]

In his farewell banquet address and in his remarks to reporters, Haig emphasized that Washington would act in the spirit of the 1979 accord establishing relations between the two nations. The Chinese stress the importance of this agreement because in it Washington recognizes Peking as the sole legal government of China and Taiwan as a part of the mainland.

On his last day of talks in Peking, Haig conferred for two hours with Communist Party Vice Chairman Deng Xiaoping, reputed to be the most powerful figure in this country, and for 90 minutes with Premier Zhao Ziyang. Neither Chinese leader made any substantive comment abnout the meetings.

A U.S. spokesman said Deng had sent greetings through Haig to Reagan, Vice President Bush and former presidents Nixon and Ford.The omission of former president Carter was unexplained.

Deng saw Haig in the Great Hall of the People, in the informal setting of overstuffed chairs in the Fukien Room, named for the Chinese province across the strait from Taiwan. A U.S. source said the meeting with Deng, considered all-important for the Haig mission, featured "straight talk" from the Chinese leader and seemed to be successful.

The premier received Haig in Zhongnanhai, the Chinese leadership compound where Mao Tse-tung and Chou En-lai lived and worked, and where only a few foreign visitors recently have been admitted. The two men and their aides met in a 200-year-old pagoda, decorated in bright Chinese red and other gaudy colors, alongside a tranquil lake.

Haig presented Zhao with a letter from Reagan inviting the premier to visit the United States at a convenient time.

Haig said there will be further exchanges later on the possibility of a trip to China by Reagan.

On Wednesday morning Haig flies to Manila to a foreign ministers' meeting of the Asociation of Southeast Asian Nations (ASEAN), five noncommunist countries friendly to the United States.

Washington Post Staff Writer Murrey Marder added from Washington:

The Polish-China questions raised yesterday go back to what very senior administration officials have raised in recent months of the Polish crisis, primarily in background talks with reporters. On the record, officials have been much more circumspect about this highly sensitive linkage issue in American global strategy. On April 4, Defense Secretary Caspar W. Weinberger, in Europe, told American reporters that "there's no linkage yet" between Soviet actions and the Reagan administration's position on arms sales to China. An aide to Weinberger later advised reporters that the word "yet" should be underlined.

Administration China specialists in Washington were startled by the stories which appeared under such headlines as "Weinberger Hints At Arming China If Poland Invaded." They regarded that as a diplomatic faux pas which would cause Peking's leaders to suspect they were being used. Weinberger told reporters they had misunderstood him, and no Polish-China "linkage" was intended or implied.

Nevertheless, just hours before Haig left Washington for Peking last Wednesday, as the Polish crisis was intensifying, a very senior Pentagon official, speaking on background, told reporters the administration was prepared to consider any Chinese requests for American arms. That time there was no overt linkage to the Polish crisis.