Federal authorities have interviewed more than 100 people in two separate investigations into the public disclosure of classified national security information, the start of a process that could take months or even years, according to officials familiar with the probes.

Law enforcement officials cautioned that they were only in the early stages of the investigations, and that they could prove inconclusive. FBI agents have already interviewed Attorney General Eric H. Holder Jr. and FBI Director Robert S. Mueller III. It is likely White House officials also will be contacted, but it remains unclear whether they have been interviewed yet.

The two investigations focus on an Associated Press article about a disrupted terrorist bomb plot by al-Qaeda’s affiliate in Yemen and a New York Times report about the Obama administration’s role in authorizing cyberattacks against Iran, according to officials who spoke on the condition of anonymity because of the sensitivity of the matter. There have been reports that authorities were probing the leaking of information about CIA drone operations, but officials said such an investigation had not been requested.

The pace of the investigations is partly driven by the large number of government officials who had access to the material that was disclosed and who now must be interviewed, officials said. But that slow pace is also butting up against increasing urgency on Capitol Hill, where Republican lawmakers are alleging that the White House has purposefully disclosed classified information to reporters to burnish President Obama’s national security credentials ahead of the November election.

Last week, Holder appointed a pair of veteran prosecutors to lead the investigations, which had been overseen by his national security division. Republican members of Congress swiftly accused Holder of a conflict of interest in his choice of U.S. attorneys Ronald C. Machen Jr. of the District and Rod J. Rosenstein of Maryland because they ultimately report to the Justice Department.

FBI agents have already interviewed Attorney General Eric H. Holder Jr. and FBI Director Robert S. Mueller III. (J. Scott Applewhite/AP)

“This is a very big deal,” Sen. Lindsey O. Graham (R-S.C.) told Holder at a Senate hearing Tuesday. “You’re handling it in a way that creates suspicions. . . . And all I’m asking is for you to find a lawyer in this country that all of us could say, ‘That is the right person to do this job,’ rather than you picking two people and telling us about how great they are.”

Holder made it clear he was not changing course.

The two investigations follow a string of federal prosecutions involving leaks of classified material during the Obama administration. The administration has launched more such prosecutions than all previous administrations combined.

The cases have included ones against a former CIA officer charged with disclosing information about agency personnel; another former CIA official charged with leaking U.S. intelligence on Iran; and a contractor at the State Department indicted for providing a reporter with classified information on North Korea.

In April 2010, former National Security Agency official Thomas Drake was charged with willful retention of classified information, obstruction of justice and false statements in a case involving alleged waste and mismanagement. And in December 2009, Sha­mai Leibowitz, a former FBI contract linguist, pleaded guilty to providing classified FBI documents to an Internet blogger.

Holder noted last week the unusual position the cases have put him in.

“We have brought more leak cases . . . than any other administration,” Holder said in testimony before the Senate Judiciary Committee. “I was getting hammered by the left for that only two weeks ago, and now I’m getting hammered by the right for potentially not going after leaks. It makes for an interesting dynamic.”

A spokesman from the Justice Department declined to comment on any aspect of the investigations.

But in addressing leak investigations more broadly, administration officials have said that their jobs have been made easier by the proliferation of technology, especially e-mail, which allows investigators to track contacts between reporters and alleged leakers. In some cases, investigators are now also able to determine which employees looked at classified material on their computers and when.

“Improved tools, including auditing measures, employee physical access or badging records and phone records, play an important role in internal investigations and aid in unmasking individuals who leak classified information,” Assistant Attorney General Lisa O. Monaco said in testimony before Congress earlier this year.

Several attorneys involved in defending alleged leakers say they think the increase in the number of prosecutions also reflects the Obama administration’s desire to establish its credentials in the intelligence community.

“This is an administration that needed to show toughness,” said Abbe Lowell, a Washington lawyer who has been involved in several leak investigation cases and is defending Stephen Kim, a contractor at the State Department who was indicted for allegedly disclosing classified national defense information to a reporter in 2010. “The leaks of classified information was low-hanging fruit. There is no constituency against leak investigations except the media. It’s an easy area to be tough in.”

Steven Aftergood, director of the Project on Government Secrecy at the Federation of American Scientists, said the investigations also reflect the “residual aftershock” of the disclosures by WikiLeaks, the anti-secrecy group.

“WikiLeaks was not one or two stories,” Aftergood said. “It was a massive hemorrhaging of classified documents that was totally outside of government control. The reaction to that has been an intense ratcheting up of security as well as a diminished tolerance for security violations.”

The Defense Department is prosecuting Army Pfc. Bradley Manning in military court for allegedly providing the material to WikiLeaks.

Aftergood said that leak prosecutions are difficult for the government because there is no official secrets law. Instead, the cases are brought under a 1917 espionage law that requires prosecutors to show the leaker intended to harm the United States with the disclosures.

And if a leak case goes to trial, it puts authorities in the position of having to acknowledge that the leaked classified information is accurate — and possibly force them to disclose even more classified material, officials said.

Staff writers Greg Miller, Carol D. Leonnig, Rosalind S. Helderman and David Nakamura and staff researcher Julie Tate contributed to this report.