WASHINGTON — By exposing the names and addresses of foreign relatives, the cybertheft of private information on U.S. security clearance holders by hackers linked to China will complicate the deployment and promotion of American intelligence professionals with special language skills and diverse backgrounds, current and former U.S. officials say.

Officials fear that China will seek to gain leverage over Americans with access to secrets by pressuring their overseas relatives, particularly if they happen to be living in China or another authoritarian country. Over the last decade, U.S. intelligence agencies have sought to hire more people of Asian and Middle Eastern descent, some of whom have relatives living overseas. The compromise of their personal data is likely to place additional burdens on employees who already face onerous security scrutiny.

China denies involvement in the cyberattack that is being called the most damaging national security loss in more than a decade.

The potential for new avenues of espionage against the U.S. is among the most obvious repercussions of the pair of data breaches by hackers who are believed to have stolen personnel data on millions of current and former federal employees and contractors.

Officials from the Department of Homeland Security, which is in charge of defending civilian government networks from cyberattacks, and the Office of Personnel Management, which failed to protect its sensitive personnel information from hackers, are slated to discuss the loss today in front of the House Oversight and Government Reform Committee.

“It may be the single biggest breach of data that our government has ever had,” Jason Chaffetz, a Utah Republican who chairs the oversight committee, said on the C-SPAN Newsmakers program.

In the cyberattack targeting federal personnel records, hackers are believed to have obtained the Social Security numbers, birth dates, job actions and other private information on every federal employee and millions of former employees and contractors.

In a second attack the cyberspies got detailed background information on millions of military, intelligence and other personnel who have been investigated for security clearances.