WASHINGTON — Chinese government hackers are suspected of breaching the computer networks of the U.S. Postal Service, compromising the data of more than 800,000 employees – including the postmaster general’s.

The intrusion was discovered in mid-September, said officials, who declined to comment on who was thought to be responsible. The FBI is leading the investigation into the hack.

The news, announced by the Postal Service, came as President Obama arrived Monday in Beijing for high-level talks with his counterpart, President Xi Jinping, as well as for an economic summit.

The Chinese government has consistently noted that Chinese law prohibits cybercrime. But China has been tied to several recent intrusions, including one into the computer systems of the Office of Personnel Management and another into the systems of a government contractor, USIS, that conducts security-clearance checks.

The intrusion into the USPS networks, officials said, was carried out by a sophisticated actor who did not appear to be interested in identity theft or credit card fraud.

“It is an unfortunate fact of life these days that every organization connected to the Internet is a constant target for cyber intrusion activity,” Postmaster General Patrick Donahoe said in a statement. “The United States Postal Service is no different. Fortunately, we have seen no evidence of malicious use of the compromised data and we are taking steps to help our employees protect against any potential misuse of their data.”

The compromised data included names, dates of birth, Social Security numbers, addresses, dates of employment and other information, officials said. The data of every employee was exposed.

No customer credit card information from post offices or online purchases at USPS.com was breached, officials said.

While the breaches could be useful to a foreign government seeking access to individuals in sensitive federal work, it is not clear why Postal Service employees would be of such interest.

Still, analysts said that a federal agency such as the USPS would make a logical espionage target for China. First, the Chinese may be assuming that the Postal Service is more like theirs – a state-owned entity that has vast amounts of data on its citizens, said James Lewis, a cyber-policy expert at the Center for Strategic and International Studies. Second, he said, China would be interested in amassing large sets of data that can be analyzed for previously unknown links or insights.

“They’re just looking for big pots of data on government employees,” Lewis said.

“For the Chinese, this is probably a way of building their inventory on U.S. persons for counterintelligence and recruitment purpose.”