WASHINGTON — Hackers linked to China appear to have gained access to the sensitive background information submitted by intelligence and military personnel for security clearances, several U.S. officials said Friday, describing a second cyberbreach of federal records that could dramatically compound the potential damage.

The forms authorities believed to have been accessed, known as Standard Form 86, require applicants to fill out deeply personal information about mental illnesses, drug and alcohol use, past arrests and bankruptcies. They also require the listing of contacts and relatives, potentially exposing any foreign relatives of U.S. intelligence employees to coercion. Both the applicant’s Social Security number and that of his or her cohabitant is required.

The officials spoke on condition of anonymity because the security clearance material is classified.

“This tells the Chinese the identities of almost everybody who has got a United States security clearance,” said Joel Brenner, a former top U.S. counterintelligence official. “That makes it very hard for any of those people to function as an intelligence officer. The database also tells the Chinese an enormous amount of information about almost everyone with a security clearance. That’s a gold mine. It helps you approach and recruit spies.”

The Office of Personnel Management, which was the target of the hack, has not officially notified military or intelligence personnel whose security clearance data was breached, but news of the second hack was starting to circulate in both the Pentagon and the CIA.

The officials said they believe the hack into the security clearance database was separate from the breach of federal personnel data announced last week – a breach that is itself appearing far worse than first believed. It could not be learned whether the security database breach happened when an Office of Personnel Management contractor was hacked in 2013, an attack that was discovered last year. Members of Congress received classified briefings about that breach in September, but there was no mention of security clearance information being exposed.

The office had no immediate comment Friday.

Nearly all of the millions of security clearance holders, including CIA, National Security Agency and military special operations personnel, are potentially exposed in the security clearance breach, the officials said. More than 4 million people had been investigated for a security clearance as of October 2014, according to government records.

In the hack of standard personnel records announced last week, two people briefed on the investigation disclosed Friday that as many as 14 million current and former civilian U.S. government employees have had their information exposed to hackers, a far higher figure than the 4 million the Obama administration initially disclosed.

The personnel records would provide a foreign government an extraordinary roadmap to blackmail, impersonate or otherwise exploit federal employees in an effort to gain access to U.S. secrets – or entry into government computer networks.