Within less than a month and without a word of explanation, China has replaced the presidents of two of its leading financial institutions -- the Bank of China and the People's Bank of China.

The official Communist Party newspaper People's Daily reported last week that Chen Muhua, the minister of foreign economic relations and trade, would leave that job to become president of the country's state-run central bank, the People's Bank of China, replacing Lu Peijian. Lu will become auditor general.

Earlier this month, it was learned that Jin Deqin had been fired as president of the Bank of China, a state-run bank specializing in overseas operations and foreign exchange transactions. Jin was replaced by Zhao Bingde, a bank vice president, who was made acting president. In answer to a query, a bank spokesman said that the changeover at the Bank of China occurred at the end of last month. No announcement was made at the time.

It was as though the chairman of the Federal Reserve and the secretary of commerce in the United States had been replaced, with one change meriting only a few lines in a newspaper report and the other coming without any announcement or report whatsoever.

It was not clear whether there was any relationship between last week's change at the People's Bank of China and the earlier top-level switch at the Bank of China. But some observers suspect that Jin had become the first high-ranking official to run afoul of the Chinese government's current anticorruption campaign. The bank spokesman said that Jin had not been assigned to another job yet. Efforts to reach Jin have failed.

Foreigners here have a special interest in Jin's case, because the Bank of China has important and far-ranging overseas branches. Jin was respected by many of the foreign businessmen and bankers working here.

After completing an assignment as the Bank of China's director in London, Jin returned to China three years ago. As president, he made the bank a more activist organization, involving it more in international lending. As one foreign trade specialist here put it, he made the bank assume a "more aggressive posture."

So Jin's ouster has become a major topic of cocktail party speculation among foreigners in Peking, with at least three unsubstantiated theories, or explanations, being offered for his firing.

What makes the speculation all the more interesting is that the Chinese government recently intensified its propaganda drive against corruption, indicating that "larger targets" should be singled out for investigation and exposure.

It is not known whether Jin's ouster will decrease confidence in China's business investment climate.

"What's important is that the government be able to make changes like this without disrupting things," said a foreign economist who had met with Jin when he was bank president. "If they can make changes pragmatically, without a lot of recriminations, then it would be reassuring. It might actually increase confidence. As the economic reforms progress, they've got to be able to discipline people."

All that is known for certain is that Jin's ouster coincided roughly with a government meeting at which leading officials began talking of the need to punish high officials engaged in "unhealthy practices."

Bo Yibo, the official in charge of the central commission for guiding the Communist Party's three-year rectification campaign, gave a speech on Feb. 28 in which he said that "to check unhealthy tendencies, we should not confine ourselves merely to "swatting flies."

In the meantime, Jin has dropped out of sight, and those who knew and respected him are stuck with three theories:

* The bonus theory: One of the "unhealthy tendencies" being pointed to in the anticorruption campaign has been "the indiscriminate issuance of money and goods," including unjustified bonuses, and Jin was said to have been generous with bonuses, according to Bank of China observers.

On March 18 in a lead news item on the drive against profiteers, the South China Morning Post in Hong Kong said that while no reason was given for Jin's ouster, the Bank of China was reported to have failed to comply with government directives ordering national enterprises to cut back on annual bonuses.

According to one unofficial account circulating here, Jin had provided pay bonuses both to top executives at the Bank of China and to section chiefs. Last year, as this unofficial account has it, each bank employe was allowed a free western-style suit, courtesy of the bank.

* The foreign exchange theory: While admitting to a lack of hard evidence, some argue that Jin must have been made the scapegoat for a rumored "serious drop" in China's foreign-exchange reserves, reported by the government last fall at $16.8 billion. But a commercial banker said that based on available evidence, the Bank of China appeared to be doing fairly well as far as foreign exchange was concerned.

* The "turf battle theory: It is conceivable that Jin's activism rubbed some more conservative Chinese banking and financial officials the wrong way. The banker could have been the victim of a power struggle with the leaders of other financial institutions, such as the People's Bank of China.