A former senior government scientist who held the highest security clearances pleaded guilty to espionage on Wednesday and agreed to a 13-year prison term for selling top-secret information on military satellites and other technology to an F.B.I. agent posing as an Israeli spy.

The scientist, Stewart D. Nozette, 54, who worked at the White House in 1989-90 and helped lead the search for water on the moon, was not charged with spying for Israel.

But Dr. Nozette consulted for a state-owned Israeli company, identified in the Israeli news media as Israel Aerospace Industries, from 1998 to 2008. The company paid him a total of $225,000 for answering technical questions it posed monthly, according to court documents.

Dr. Nozette, who holds a Ph.D. in planetary sciences from the Massachusetts Institute of Technology, told the undercover agent that he had believed the company was a front for Israeli intelligence.

The plea deal ends the espionage case against one of the highest-ranking American scientists ever charged with trying to spy for a foreign power. Israel Aerospace Industries did not respond to a request for comment. The investigation did not allege that Israel or anyone acting on its behalf committed any offense, the Justice Department said.

Dr. Nozette worked at the White House on the National Space Council in 1989 and 1990 and as a physicist for the Department of Energy’s Lawrence Livermore National Laboratory from 1990 to 1999. He worked on the “Star Wars” missile defense project and held a “Q” clearance, giving him access to the nation’s most guarded nuclear secrets.

He helped develop the Clementine satellite, which used radar to detect what appeared to be ice at the moon’s south pole in 1994. Later, Dr. Nozette served as president, treasurer and director of the Alliance for Competitive Technology, a nonprofit enterprise that developed technology for several government agencies.

In 2007, federal agents searched Dr. Nozette’s home in Chevy Chase, Md., as part of a fraud investigation and found classified documents, according to a statement of facts filed in court on Wednesday. In January 2009, in a case unrelated to the espionage investigation, Dr. Nozette pleaded guilty to fraud and tax evasion and agreed to pay $265,205 in restitution to the government.

By then, the F.B.I. had discovered a 2002 e-mail in which Dr. Nozette had threatened to take an unidentified classified program to Israel or another, unnamed country. Court documents did not reveal to whom the e-mail was sent.

In September 2009, the undercover F.B.I. agent called Dr. Nozette and arranged to meet him at the Mayflower Hotel in Washington, where the agent said he worked for the Mossad, the Israeli intelligence agency. Dr. Nozette replied, “Good. Happy to be of assistance,” according to the statement of facts. The scientist told the agent, “I thought I was working for you already.”

The undercover agent told Dr. Nozette that they could communicate via post office box and gave him a “clean phone” to use for secure communications. Dr. Nozette later provided top secret information about satellites and other technology. He told the agent he had passed on “some of the most classified information there is,” declaring, “I’ve sort of crossed the Rubicon.”

Dr. Nozette eventually asked for $2 million and an Israeli passport.

When agents arrested Dr. Nozette at a Washington hotel in October 2009, he excused himself and went to the bathroom, where he hid — inside the toilet tank — $10,000 in cash he had just received from the supposed spy.