The Obama White House’s war against leaks, and its penchant for secrecy and noted lack of transparency, are the worst “since the Nixon administration,” according to a major new study that relied on interviews from leading Washington reporters and news organization chiefs.

The report, released Thursday by the Committee to Project Journalists, found that reporters from many major media outlets consider the Obama administration the most closed-off in recent memory, and that there is not “any precedent” for its often hostile relationship toward the press.

More than 30 veteran reporters were interviewed for the piece, which was written by CPJ’s Leonard Downie Jr., former executive editor of The Washington Post and now a professor at Arizona State’s Walter Cronkite School of Journalism and Mass Communication.

The massive study goes into great detail in discussing the administration’s battle against leakers such as Edward Snowden; its “Insider Threat Program” that asks government employees to monitor their colleagues’ behavior; and general lack of transparency, despite repeated promises from Mr. Obama that his White House would be the most open in history.

“This is the most closed, control freak administration I’ve ever covered,” wrote New York Times Washington correspondent David Sanger, one of the journalists interviewed for the report.

At least six government employees and two contractors — including Mr. Snowden — have been subjects of felony criminal prosecutions since 2009, when Mr. Obama came to power.

Other investigations are under way, and notable instances of White House press crackdowns have included Justice Department subpoenas of reporters’ phone logs and emails; the inspection of Associated Press phone records; the accusation that a Fox News reporter was an “aider, abettor and/or conspirator” of an indicted leak defendant.

As a result, top journalists now say “officials are reluctant to discuss even unclassified information with them because they fear that leak investigations and government surveillance make it more difficult for reporters to protect them as sources.”

“I worry now about calling somebody because the contact can be found out through a check of phone records or emails,” said veteran journalist R. Jeffrey Smith, who now works at the Center for Public Integrity, a nonprofit government accountability news group. “It leaves a digital trail that makes it easier for the government to monitor those contacts.”

Another reporter said there is a “real problem” with the way the Obama administration deals with the press. Another is quoted as saying this White House is one of “unprecedented secrecy and unprecedented attacks on the press.”

But the White House continues to defend its behavior.

Press secretary Jay Carney was interviewed for the study, and he said “the idea that people are shutting up and not leaking to reporters is belied by the facts.”

White House national security adviser Ben Rhodes also disputed the report’s findings.

“We make an effort to communicate about national security issues in on-the-record and background briefings by sanctioned sources. And we still see investigative reporting from nonsanctioned sources with lots of unclassified information and some sensitive information.”