China, reiterating that it "resolutely opposes" arms sales to Taiwan, pressed the U.S. government today to explain its decision to sell military spare parts to the breakaway island.

While Chinese diplomats buttonholed American Embassy officials in Peking, the Foreign Ministry issued a statement saying that China's firm stand against arms sales to Taiwan "is clear-cut and consistent."

"China is urging the U.S. government to clarify its decision to sell arms spare parts to Taiwan," said a spokesman for the ministry.

The brief remarks, coming less than a day after the State Department announced plans to sell Taiwan at least $25 million in spare parts, were seen as a cautious initial response while Peking mulls its options.

The next few days are expected to provide a key test of Peking's resolve on the long-smoldering issue. Until now, Chinese officials have declared opposition to all U.S. arms sales to Taiwan, which they consider to be part of China.

Officials now will be forced to define whether American sales to replace existing parts in Taiwan's arsenal fall into an acceptable category, or constitute a serious enough offense to warrant the kind of warnings Peking has been making.

Selling spare parts to Taiwan meets the minimal demands of the island's Nationalist Chinese leaders who long have sought an advanced fighter plane to bolster their small but well-trained military against China's 4-million-man Army.

Since President Reagan entered office last year, Peking has warned of a "strong reaction" should the new administration sell a new fighter to Taiwan -- a decision that the State Department claims has not yet been made.

For months, Chinese officials refused to clarify the threat. Instead they cited what is known as "the Dutch case," or China's downgrading of relations with the Netherlands after it sold Taiwan two submarines earlier this year.

Lately, however, the warning has been refined. Foreign officials visiting China have been told that Peking would lower diplomatic relations to the level of charge d'affaires if a new U.S. fighter were sold to Taiwan.

Chinese officials reportedly have emphasized in these meetings with visitors that the strategic benefits of close ties with the United States do not override the vital issue of national sovereignty posed by Taiwan.

China considers U.S. arms sales to Taiwan an intervention in Chinese domestic affairs blocking Peking's efforts to persuade its old rivals to reunite with the communist mainland after 32 years of separation.

China has tried to convince the White House of this logic in a series of high-level meetings capped by Premier Zhao Ziyang's October talks with Reagan at Cancun and Foreign Minister Huang Hua's visit to Washington last month.

The Chinese side emerged from these talks with disappointment, according to diplomatic sources, and Peking's persistent lobbying has given way in the past weeks to a stiffening of position.

Official press commentaries have moved from logicial rebuttals of the pro-Taiwan lobby to shrill attacks against advocates of weapons sales to the island.

Although Peking began criticizing U.S. foreign policy in the Third World as far back as June and resumed the derogatory label of "superpower" to describe Washington, Chinese scoldings have grown fiercer recently.

A sure sign of Peking's disenchantment is the recent comparison of American behavior with that of China's archenemy, the Soviet Union.

When news reports from Washington suggested that uranium that had been sold to South Africa originated in China, the official press commentator in Peking charged that the two superpowers were performing a "duet" in spreading the story.

Responding to an American newspaper column urging that Reagan not be cowed by China in formulating U.S. policy toward Taiwan, the commentator leveled another blast:

"The idea that the United States has a right to meddle in China's affairs reminds people of the theory of limited sovereignty invented by Soviet President Leonid Brezhnev," said the commentator. "What a resemblance between the two." in formulating U.S. policy toward Taiwan, the commentator leveled another blast:

"The idea that the United States has a right to meddle in China's affairs reminds people of the theory of limited sovereignty invented by Soviet President Leonid Brezhnev," said the commentator. "What a resemblance between the two."