Two Chinese diplomats have been expelled from the United States after being detained last week by the FBI on suspicion of espionage, administration sources said yesterday.

State Department spokesman Phyllis Oakley said at a news briefing, "On Dec. 22, the Department of State asked the Chinese Embassy to arrange the departure from the United States of two Chinese diplomats. The two individuals were engaged in activities incompatible with their diplomatic status. I understand that they have left the United States."

Oakley said that the two were the first Chinese diplomats asked to leave the United States since formal diplomatic relations were established with the People's Republic of China in January 1979. But she said the incident has not damaged the two countries' relations.

Oakley would not provide further details on the identities of the two men or on the activities in which they were allegedly involved. Their expulsion was first reported yesterday by The Washington Times.

Wu Zurong, a second secretary in the press office of the Chinese Embassy, indicated that two Chinese diplomats had recently returned to China, but he denied that there was any problem with the U.S. government. "I have no knowledge of this. We have two diplomats who left for China a few days ago after having finished their tenure in the United States," Wu said.

He identified the two men as Hou Desheng, an assistant military attache, and Zhang Weichu, the Chinese consul in Chicago.

Asked about the condition of U.S.-Chinese relations after the incident, Oakley said, "The same as they were. There is no change in the relationship."

Justice Department sources said the men were detained early last week after one of them, an assistant military attache at the Chinese Embassy here, accepted what he believed were classified documents. Because the two have diplomatic immunity, they could not be formally arrested or charged with espionage. The sources said the detentions followed a long investigation by the FBI's local office here.

Lane Bonner, a spokesman for the FBI, refused to comment on the case.

Administration sources said yesterday that details of the case were being closely guarded because the State Department is anxious not to damage improving relations between the United States and China.

But Oakley said the United States is not trying to minimize the incident. "In no way are we trying to downplay it. When such a case arises, we deal with it promptly in accordance with established procedures," she said.

She said that "in this case, we went immediately to the Chinese government that arranged for their departure, so that . . . it wasn't necessary to declare them persona non grata."

Asked about possible retaliation by the Chinese, she said, "I'm not going to speculate on any possible retaliation by the government of China. I would add, however, that there would be no justification for retaliation." She added that there has been no protest from the Chinese government.

Sources said one of the men was picked up at a Chinatown restaurant here as he was meeting with a double agent working for the United States. No details could be learned of the circumstances under which the second person was detained.

On Dec. 17 the FBI detained Mikail Katkov, a Soviet diplomat assigned to the United Nations. Katkov, who also had diplomatic immunity, was quickly expelled. That incident was also treated delicately by the State Department because it came a week after President Reagan's summit here with Soviet leader Mikhail Gorbachev.

Oakley said the Soviets have not protested the Katkov expulsion.

A State Department official, who asked not to be identified, said the United States had hoped the matter would not become public. The official said the government is concerned about the possibility that the Chinese might take retaliatory action and expel some U.S. diplomats from China.

"We consider this matter closed," the official said. "Publicizing the names of foreign diplomats who depart the United States after having been found to have engaged in activities incompatible with their status is the exception rather than the rule."

Other sources, however, said that in previous cases, which generally have involved Soviet diplomats, the names of the persons expelled have been readily available.Staff writer Don Oberdorfer contributed to this report.