The Chinese government has made a new offer to cooperate with the incoming Reagan administration but has coupled it with a sharp warning that the approval of new arms sales to Taiwan by Washington will endanger Chinese-American diplomatic ties.

In the first extended comment by a senior Chinese official on Sino-American relations since Ronald Reagan's election, Vice Foreign Minister Zhange Wenjin acknowledged in an interview this week that China was concerned that the United States might go too far in selling new arms to Taiwan after the change of administrations in Washington Jan. 20.

On another subject, Zhang indicated for the first time publicly that China is prepared to lessen its political support for the Khmer Rouge forces of Pol Pot if this move would induce Vietnam to end its military occupation of Cambodia. But he ruled out a deal that would totally exclude the Khmer Rouge.

Zhang, the Foreign Ministry's top official on American affairs, made the remarks in a relaxed 90-minute interview in a reception room of the Chinese Foreign Ministry. The diplomat put one condition on his comments, which were conveyed through a translator, by asking that they not be placed in direct quotation.

Washington's response to Taiwan's direct appeal to the American president-elect earlier this month for more sophisticated fighter aircraft was cited as one of several potential problem areas in foreign policy that Peking will be watching to determine the new administration's overall intentions. Others included:

Expanded military cooperation with Peking. Zhang said China needs modern defense technology to counter Soviet expansionism in Asia and hopes the United States will make it available soon.

Continued U.S. encouragement of Japan to continue increasing its defense spending.

Increased pressure on Vietnam to get out of Cambodia and more support for Cambodian resistance forces, which could benefit by uniting behind someone other than Pol Pot.

A new American determination to confront what Zhang described as the Soviet drive south into the Persian Gulf and the Middle East. He said the Reagan administration should show more understanding for the Arab case if it wants to bring peace to the Middle East.

Zhang laid repeated and heavy emphasis on China's desire to cooperate with a Reagan government on a global scale to combat Soviet aggression. Some old friends of China in the Republican Party had assured him that there would be no deterioration in relations and no change on U.S. policy toward Taiwan despite Reagan's compaign call for upgrading contacts with the island government, he said.

He declined to identify the Republicans he had in mind, but other sources here noted that George Bush, Reagan's running mate and former head of the American liaison office in Peking, visited China during the campaign in a bid to reassure the Chinese about Reagan's intentions.

Zhang confirmed that recent press statements offering to work with Reagan despite his campaign promises of closer ties with Taiwan constitute an official hope that the new administration as one of its first actions will reaffirm the 1979 agreement that normalized relations and the Shanghai communique of 1972, which formally ended three decades of hostility.

But he indicated that China believes it is the time for ending all American arms shipments to Taiwan, and that any increase in the sophistication of arms delivered will seriously affect the ties between Washington and Peking.

The Carter administration resumed arms deliveries to Taiwan this year after a one-year pause but delayed action on requests for more advanced fighter aircraft that were backed by several of Reagan's key supporters in the Senate. An American defense contractor, however, has been given permission to discuss with Taiwan the possible sale of FX intermediate-range fighter planes.

Echoing commentaries issued earlier this year by the official New China News Agency, Zhang said that any arms deliveries at all violated the normalization agreement, which Zhang helped negotiate. He said that the United States had told Peking that the problem of arms deliveries to Taiwan would disappear with the passage of time.

The Chinese diplomat then appeared to sound a strong and specific new warning by saying that China hoped the United States would not go too far in new arms sales for Taiwan.

Americans who think China is so frightened of the Soviet Union that it will accept any move the United States makes are seriously mistaken, he said. wU.S. officials had to be aware that the benefits of normalization are as important for America as for China, he said, and had to see Sino-American relations, in a strategic context.

At several points in the interview, Zhang, who has served as his country's ambassador to Canada and is an authoritative spokesman on foreign policy, emphasized China's desire to undertake parallel actions with the United States and its allies and with Third World countries in opposing Soviet advances in the Far East and elsewhere.

He did not offer specifics, but he said at one point that meeting the Soviet global military threat was the basis for the relations between the United States and China.

He also returned several times to the continuing war in Cambodia, saying the United States had to pressure Vietnam and the Soviet Union to seek an end to the war.

China has strongly supported the Khmer Rouge since Vietnam's 1979 invasion of its Southeast Asian neighbor. But visits here in recent weeks by the prime ministers of Thailand and Singapore suggest that Peking is having trouble getting other countries to continue extending diplomatic recognition to the Pol Pot govrnment because of its controversial human rights record.

China has frequently said that it was up to the Cambodians to choose their own leaders, but Zhang made that position more specific by saying, in response to a question, that it might be better now for Prince Norodom Sihanouk, ousted as ruler in 1970, or Son Sann, a former noncommunist prime minister, to take charge of the Cambodian resistance forces.

Son Sann, an aging banker who has spent most of his 10-year exile in Paris, is reported by foreign sources to have visited Peking recently and to have won new support from the Chinese.

Sihanouk, who lives alternately in Peking and North Korea, is said by sources to have refused Chinese suggestions that he reenter Cambodian politics, saying the time was not yet right for his return.

China has supported the uniting of all the Cambodia resistance groups, but leadership by Khmer Rouge of the unified movement is not a precondition, Zhang said. This represents a considerable move from past public statements in which the Chinese have insisted that Khmer Rouge leadership was essential to maintain the military strength of resistance forces.

Nevertheless, Zhang insisted, China disagrees with the viewpoint, apparently gaining favor in other friendly Asian nations, that all support should be withdrawn from the Khmer Rouge in a bid to gain broader international backing for the struggle against Vietnam.