The diplomat, David M. Satterfield, was identified in the indictment as a United States government official, "USGO-2," the people briefed on the matter said. In early 2002, USGO-2 discussed secret national security matters in two meetings with Steven J. Rosen, who has since been dismissed as a top lobbyist for the American Israel Public Affairs Committee, known as Aipac, who has been charged in the case.

The indictment said that Mr. Rosen met USGO-2 on Jan. 18, 2002, and March 12, 2002, but provides few details about the encounters. The indictment does not describe Mr. Satterfield's activities in detail nor does it specify what classified information the diplomat discussed with the lobbyist. The meetings were also confirmed by documents, people who have been briefed said. These people asked not to be identified because many of the matters related to the case are classified.

The indictment does not accuse USGO-2 of any wrongdoing, nor does it indicate whether he might have been authorized to talk with the lobbyist. Mr. Satterfield is not believed to be the subject of a continuing investigation. He is the first higher-ranking government official to be caught up in the criminal inquiry.

Mr. Satterfield's role in the inquiry has been known within a small circle at the State Department. Before he was sent to Baghdad, officials at the State Department asked the Justice Department whether the investigation posed any impediment to his assignment in Iraq, someone who has been officially briefed said. Officials at the State Department were advised that he could take the job.

Mr. Satterfield is one of the department's rising stars. Before his assignment as deputy chief of mission in Baghdad, Mr. Satterfield, 50, held several jobs in the Clinton and Bush administrations as a Middle East expert. He was ambassador to Lebanon from 1998 to 2001, and was confirmed by the Senate as ambassador to Jordan in 2004, although he never served in that position.

Current and former colleagues say that Mr. Satterfield, who went to Iraq earlier this year, chose the Baghdad post because it posed a bigger professional challenge than Jordan. The United States ambassador to Iraq, Zalmay Khalilzad, has strong political credentials but, colleagues said, Mr. Satterfield was brought in to provide managerial strength.

Mr. Satterfield did not respond to an e-mail message asking about his role in the case, and one State Department spokesman said that Mr. Satterfield would not discuss the matter. Sean McCormack, the spokesman for the department, referred legal questions about Mr. Satterfield to the Justice Department.

He added, "David is a fine public servant who has served the American people for many years and is continuing to do so under difficult working conditions."

The investigation is one of the more puzzling national security cases in recent years, focusing on the interactions between foreign affairs lobbyists and officials of the United States and other governments, who over the years, have routinely traded gossip and sometimes classified information. Under the Justice Department's theories of the case, it is no longer clear whether such conversations are legally permissible.

Current and former colleagues praised Mr. Satterfield as a seasoned and careful diplomat. "I've known David Satterfield for 20 years, and he is thoroughly professional, and takes his responsibilities very seriously," said Dennis Ross, the former chief Middle East negotiator for the United States and a longtime State Department official. "He has always acted solely in American interests." Martin Indyk, Mr. Satterfield's former boss in the Clinton administration, both at the National Security Council at the White House and at the State Department, said the idea that Mr. Satterfield leaked classified information is "absurd."

"The way he speaks is crafted for a public audience," Mr. Indyk said. "He has this facility for talking publicly without saying anything sensitive. So the idea that he would be leaking classified information is preposterous.

"He has an unblemished record as the consummate diplomat and as a highly effective policy maker as well. He is among the cadre of the best and the brightest in the Near East Bureau. He dealt with Aipac, because it was part of his job to deal with Aipac."

Mr. Rosen and another former lobbyist, Keith Weissman, have been charged with conspiring to communicate national defense secrets to journalists and a foreign government, which officials have identified as Israel. A third person, Lawrence A. Franklin, a former Pentagon analyst and Iran expert, has also been charged, accused of turning over information to the two lobbyists.

At an arraignment on Tuesday in Federal District Court in Alexandria, Va., all three pleaded not guilty and were released on their own recognizance. Judge T. S. Ellis III set a trial date for Jan. 3.

Only Mr. Rosen met with USGO-2, according to the indictment. At the time of the meetings, Mr. Satterfield was the deputy assistant secretary for Near Eastern and South Asian affairs, which made him the State Department's second-ranking official for the Middle East.

Their meetings are listed as overt acts in a conspiracy to illegally communicate national defense secrets to a foreign government. After Mr. Rosen's first meeting with USGO-2 on Jan. 18, 2002, the indictment said, a memorandum containing the information that Mr. Rosen had obtained was sent to other Aipac employees. The indictment did not indicate who wrote the memorandum, but said that it "contained classified information provided by USGO-2."

The two men met again on March 12, the indictment said. At their second meeting, they talked about Al Qaeda, the indictment said, without saying what aspect of the terror network was discussed. On March 14, Mr. Rosen disclosed to an unidentified foreign official, "FO-2," the information that he had heard from USGO-2, the indictment said.

Prosecutors have charged that Mr. Rosen and Mr. Weissman improperly obtained classified information from Mr. Franklin, Mr. Satterfield and two other American officials. The two officials whose identities remain unclear are referred to in the indictment as "USGO-1," and a Defense Department employee identified as "DOD-B." Although USGO-1 has not been publicly identified, the people who have been officially briefed said that person was no longer in the government.

As the Aipac's director of foreign policy issues, Mr. Rosen was a well-known figure in foreign policy circles related to the Middle East, inside and outside the government. He helped Aipac set its lobbying goals and maintained relationships with powerful conservatives in the Bush administration. Mr. Weissman was a senior Middle East analyst.

Several Middle East experts noted that Mr. Satterfield was never regarded as particularly supportive of Aipac's views on Israel. One analyst at an independent consulting firm recalled attending a conference Aipac held for Congressional staff members, during which Mr. Satterfield talked about United States policy toward Israel. She recalled that Mr. Satterfield was met with a mixed reception because his comments were not in line with Aipac's views.