The list of relatives and “close or continuous contacts” is a standard part of the forms and interviews required of American officials every five years for top-secret and other high-level clearances, and government officials consider the lists to be especially delicate.

In 2010, when The New York Times was preparing to publish articles based on 250,000 secret State Department cables obtained by WikiLeaks, the newspaper complied with a request by the department to redact the names of any Chinese citizens who were described in the cables as providing information to American Embassy officials. Officials cited fear of retaliation by the Chinese authorities.

Officials say they do not know how much of the compromised data was exposed to the Chinese hackers. While State Department employees, especially new ones, are required to list all their foreign friends, diplomats have so many foreign contacts that they are not expected to list them all.

But other government officials are frequently asked to do so, especially in interviews with investigators. The notes from those interviews, conducted by a spinoff of the personnel office called the United States Investigative Service, were obtained by hackers in the earlier episode last year.

Intelligence agencies use a different system, so the contacts of operatives like those in the C.I.A. were not in the databases.

But the standard form that anyone with a national security job fills out includes information about spouses, divorces and even distant foreign relatives, as well as the names of current or past foreign girlfriends and boyfriends, bankruptcies, debts and other financial information. And it appears that the hackers reached, and presumably downloaded, images of those forms.

“I can’t say whether this was more damaging than WikiLeaks; it’s different in nature,” said Representative Adam B. Schiff, a California Democrat who is a member of the House Intelligence Committee, which was briefed by intelligence officials, the Department of Homeland Security and the personnel office on Tuesday. Mr. Schiff, who declined to speak about the specifics of the briefing, added, “But it is certainly one of the most damaging losses I can think of.”