The Pentagon and Lockheed Martin Corp, its top supplier, discounted a Wall Street Journal report that cyber spies had stolen secrets of the F-35 Joint Strike Fighter aircraft being built for the United States and nearly a dozen allies.

I'm not aware of any specific concerns, Bryan Whitman, a Defense Department spokesman, said of the reported compromise of the Pentagon's costliest arms acquisition plan.

He spoke after the Journal said on Tuesday that terabytes of data about the plane's design and electronics had been taken, according to current and former officials said to be familiar with the matter.

Former U.S. officials were cited as saying the alleged cyber espionage appeared to have come from China. A Chinese embassy spokesman did not immediately respond to a request for comment from Reuters.

Such computer intrusions, if confirmed, could make it easier to defend against the multirole F-35, a roughly $300 billion program in the early stages of production. The United States alone plans to buy 2,443 of three F-35 designs for its Air Force, Navy and Marine Corps.

The radar-evading aircraft is being developed with financing from the United States, Britain, Italy, the Netherlands, Turkey, Canada, Australia, Denmark and Norway. Other projected early buyers include Israel and Singapore.

Lockheed Martin, the primary contractor, said, We actually believe the Wall Street Journal was incorrect in its representation of successful cyber attacks on the F-35 program.

I've not heard of that, and to our knowledge there's never been any classified information breach, Bruce Tanner, the company's chief financial officer, said during a teleconference on the company's latest earnings.

The Wall Street Journal is standing by its story, according to Robert Christie, a spokesman for the newspaper's publisher, Dow Jones & Co, which is owned by News Corp.

Tanner acknowledged attacks on Lockheed Martin's systems, much like those on U.S. government networks, are continuous.

We do have stringent measures in place to both detect and stop these attacks, he said.

Later, the Defense Department said it did not comment on alleged or actual cyber infiltrations, potential impacts to DoD operations, or any possible investigations.

This was to deny information on a potential success or failure that might help an attacker, said Lieutenant Colonel Eric Butterbaugh of the Air Force, a department spokesman.

Lockheed's chief subcontractors on the F-35 are Northrop Grumman Corp and BAE Systems Plc. Representatives of Northrop and BAE referred questions to Lockheed.

Last October, the Pentagon's chief internal watchdog office withdrew a finding that U.S. technology in the F-35 might have been compromised by unauthorized access at units of BAE Systems.

In a rare climbdown, the inspector general's office said in an October 23-dated statement that it had lacked sufficient appropriate evidence to support the conclusion of a March 6 report in which it had raised alarm about the security oversight of BAE facilities and computers.

The withdrawn report had noted that BAE was also playing a key role in the Eurofighter Typhoon, a competitor to the F-35 for billions of dollars in overseas sales.

EADS, with a 46 percent stake, is the largest shareholder in the Typhoon-building consortium, Eurofighter GmbH, based in Halbergmoos, Germany. BAE has 33 percent and Italy's Finmeccanica SpA holds 21 percent through its Alenia Aeronautica unit.

The Defense Science Board, a Pentagon advisory panel, said in a just-released report that the U.S. Defense Department was not yet organized, trained, equipped or in many cases adequately focused on threats to cyberspace-enabled operations.

A task force formed by the board concluded in the March-dated report that threats from cyber-intelligent adversaries represent a clear and present danger to U.S. national security in the absence of tightened cyber security plans.

(Additional reporting by David Morgan, Karen Jacobs, Andrew Gray)

(Writing by Jim Wolf; Editing by Phil Berlowitz)