Nearly two weeks after it vigorously protested U.S. plans to continue coproduction of the F5E fighter with Taiwan, China has considerably toned down its criticism and gone back to business as usual in its handling of Chinese-American relations.

Although the official news media continue to criticize the U.S. decision, commentaries have been confined to legal arguments free of the invective and threats that were common just a short time ago. All suggest the need for further discussions to settle the matter.

U.S. diplomats in Peking who nervously joked about packing their bags when the decision leaked out Jan. 11 report little tension in their dealings with Chinese. Visas for official delegations seeking to visit the United States continue to be processed at normal rates and scholarly programs remain unaffected.

Chinese officials invited U.S. diplomats to the Foreign Ministry last week not to hear a protest, but to shake hands at a ceremony marking the ratification of the first consular convention between the two nations since they normalized diplomatic relations three years ago.

Although some American businessmen complain of anti-American sentiment from Chinese trade officials, other companies say the issue has not been raised in their talks with government regulators.

"The Chinese reaction has been measured, and with good will on both sides, we're reasonably optimistic," a senior U.S. official said last week. "There's been no adverse ruboff yet and we hope there won't be."

Some diplomats believe the Chinese response shows that Peking is trying to defuse the issue, satisfied that it stopped Washington from selling more advanced aircraft sought by Peking's foes on Taiwan.

Other foreign analysts warn that the restrained Chinese stance thus far may be a calm before the storm while top leaders mull their choices and press for further concessions from the United States.

Even though President Reagan's decision to extend the F5E coproduction line with Taiwan was billed as a compromise in Washington, China does not credit the administration for forswearing sales of more sophisticated aircraft sought by the Nationalist government on Taiwan.

Peking regards Taiwan as a Chinese province and any arms sales to the breakaway island as an intervention into China's domestic affairs. Before Reagan's decision, Peking demanded a U.S. recognition of that principle as a minimum condition for maintaining good relations.

Analysts believe that Peking was given hope of some kind of American concession during talks with Assistant Secretary of State John Holdridge, who was sent here Jan. 11 to explain U.S. plans for its old allies on Taiwan. He reportedly told Chinese officials that exactly what the Americans sell and for how long remain "an open question."

Chinese negotiators are thought to have seen this as a sign of flexibility on the U.S. side, said foreign analysts. It is believed to have been seized upon by Americanists in the Chinese leadership who are seeking some form of U.S. gesture to offset charges by conservative forces that Washington is playing fast and loose with China's sovereignty.

"The American supporters in the leadership don't want to junk the relationship with Washington," said an Asian diplomat, "but the U.S. side has painted them into a corner."

One well-informed Chinese source who favors close ties with the United States said China's top leaders, including Deng Xiaoping, could never survive politically if they acquiesced to American arms sales to Taiwan.

He said, however, that he is optimistic that continuing talks will resolve the issue and remind both sides of the strategic benefits of good relations in meeting the challenge of a common enemy, the Soviet Union.

"When we quarrel," he said, "the only one who wins are the Russians."

China's patience is limited, he said, partly because of "pressures" from Chinese hard-liners who believe the nation has lost face and credibility by backing off threats to downgrade diplomatic relations if Washington continues its arms policy toward Taiwan.

"Some Politburo members who were unsure about normalization in 1979 must see this as the great American betrayal," said one Western diplomat.

The official media's recent depiction of Washington as a double-dealing hypocrite with aggressive foreign policy behavior like the hated Russians increases the pressure on Peking authorities to criticize the Americans if they do not give in, said diplomats.

Chinese officials pride themselves on executing a foreign policy based on "doing what we say we will do" even at great self-sacrifice. When their warnings were ignored, they say, Chinese troops entered the Korean War in the 1950s, fought India in the 1960s and invaded Vietnam in the 1970s.

Another problem arises because China downgraded its diplomatic relations with the Netherlands last year after the Dutch government decided to sell two submarines to Taiwan. If Peking backs down to the larger U.S. government, it believes face would be lost, analysts said