The Republican chairmen of the two House committees with NASA oversight responsibility have charged publicly that senior leadership at the space agency may have been involved in the leak of classified information to China and other nations, and that a federal criminal probe into the charges has been dropped under “political pressure.”

The charges were raised Feb. 8 in letters to FBI Director Robert Mueller and Michael Horowitz, the Justice Department’s inspector general, jointly signed by Reps. Frank Wolf (R-Va.) and Lamar Smith (R-Texas) who chair the House Appropriations Commerce, Justice, Science and Related Agencies subcommittee and the House Science, Space and Technology Committee, respectively.

“We have been informed of an investigation that the Federal Bureau of Investigation (FBI), the NASA Office of the Inspector General and other law enforcement agencies have been working on since 2009 relating to the alleged illegal transfer of ITAR-controlled technology by individuals at the NASA Ames Research Center,” the lawmakers wrote, referring to the International Traffic in Arms Regulations. “It is our understanding that this illegal technology transfer may have involved classified Defense Department weapons system technology to foreign countries, including China, potentially with the tacit or direct approval of the center’s leadership.”

According to sources at Ames and on Capitol Hill, the case involves Ames Center Director Simon P. “Pete” Worden and members of the center’s staff who are not U.S. citizens. Among the technology in question is a propulsion system originally developed for missile defense applications that was adapted for NASA’s Lunar Atmosphere and Dust Environment Explorer (Ladee). Now entering thermal vacuum test at Ames, Ladee is a robotic mission designed to study the Moon’s thin atmosphere and conditions near its surface from an equatorial orbit. It is scheduled for launch this summer.

Among the charges mentioned in the congressional letters are allegations that the protected technology information has been disseminated in public conferences overseas “with Chinese and other foreign officials present,” and that information-protection “safeguards may not have been used or may have explicitly been ignored on multiple occasions” at Ames.

Worden, a former Air Force brigadier general with a reputation as a bureaucratic entrepreneur, has been the target of unsubstantiated allegations along the lines mentioned in the congressional letters since last summer. He is known to maintain a free-wheeling culture of innovation at Ames, encouraging young engineers and scientists regardless of their nationality to develop new ideas.

But Smith, who is just taking over as chairman of the science panel that authorizes NASA spending, and Wolf, a veteran appropriations subcommittee chair who has blocked NASA from spending any money for space cooperation with China on human-rights grounds, also charged that a computer hard drive confiscated from one member of Worden’s staff was “corrupted, as were all the backup copies in the government’s possession.” In addition to that suggestion of a cover-up, which a congressional staffer said may have occurred while the hard drive was in the possession of the NASA inspector general, the two chairmen also implied that the Justice Department blocked prosecution of the case for reasons that go beyond evidence and legal judgment.

“We were very concerned to learn earlier this week that despite the U.S. Attorney’s request for permission from the Justice Department to proceed with indictments, this request was recently denied without explanation, despite the backing of both the FBI and the U.S. Attorney’s office,” they wrote. “We are deeply concerned that political pressure may be a factor and are formally requesting an investigation into the circumstances of the Justice Department’s actions with regard to this case.”

Asked where any political pressure might have originated, one congressional staffer said Friday, “I have every reason to believe, based on information I’ve seen, that Worden has a history of leveraging his supporters who may have connections with the White House or senior NASA management to intervene on his behalf.”

The lawmakers noted that an assistant U.S. attorney in California was reassigned off the case, and that the statute of limitations on one potential criminal charge expired on Dec. 15, 2012. Wolf, whose subcommittee also controls FBI funding, first raised the issue with the investigative agency that month, according to the letter sent to Mueller.

“I think you’ve had violations of the law,” Wolf told Aviation Week Friday. “You’ve had the FBI look at this. You’ve had the U.S. attorneys make a decision to move ahead, and you’ve had somebody stop it at the Justice Department. I think you have a criminal, and a scandal here.”

NASA declined comment on grounds “it would be inappropriate for us to discuss any possible investigation,” according to a spokesman, who referred the query to the Justice Department.

A Justice Department spokesman said, “We are aware of and reviewing the letters. However, as a matter of longstanding policy, the Justice Department does not comment on whether a particular person or entity might be under investigation.”