“It is fitting that she now stands to lose both her citizenship and her liberty,” Assistant Attorney General Kenneth L. Wainstein said in an announcing the guilty plea, which was entered in federal district court in Detroit.

Mr. Wainstein, who runs the Justice Department’s national security division, said that Ms. Proudy “engaged in a pattern of deceit to secure U.S. citizenship, to gain employment in the intelligence community and to obtain and exploit her access to sensitive counterterrorism intelligence.”

She pleaded guilty to one count each of criminal conspiracy, which has a maximum penalty of five years in prison and a $250,000 fine; unauthorized computer access, which has a maximum penalty of one year in prison and a $100,000 fine, and naturalization fraud, which has a maximum penalty of 10 years in prison and a $250,000 fine.

In her plea agreement, Ms. Proudy, who lived mostly recently in Vienna, Va., close to C.I.A. headquarters in Langley, Va., acknowledged that her crimes began shortly after she entered the United States from Lebanon in June 1989 on a one-year student visa.

She acknowledged that after overstaying her visa, she had offered money to an unemployed American man to marry her in 1990, which allowed her to remain in the United States as his wife, although the couple never lived together.

She then submitted a series of false and forged documents to obtain American citizenship, which she was granted in 1994. She obtained a divorce the next year and worked in a series of jobs, including as a waitress and hostess in a chain of restaurants in the Detroit area owned by her brother-in-law, Talal Khalil Chahine, who is a fugitive from federal charges in Michigan of tax evasion in a scheme to funnel millions of dollars from his business to people in Lebanon.

In 1997, she was hired as a special agent of the F.B.I., which has been under pressure for years to hire more agents and other employees who speak Arabic for terrorism investigations. She was assigned to the bureau’s Washington D.C. field office, given a security clearance and placed in “an extraterritorial squad investigating crimes against U.S. persons overseas,” the Justice Department said in a statement to reporters.