Lockheed said parallel work on the lower-risk BAE helmet would ensure that a useable option was available in 2014.
Lockheed is also providing an F-35 jet to allow dedicated testing of the helmet in coming weeks, the sources said.
Lockheed officials, who were not at the Pentagon meeting, said on Monday that technological challenges facing the program were being addressed, and the program was making good progress.
“These kinds of challenges are normal in a developmental program,” said Steve O’Bryan, Lockheed vice president for F-35 business development.
He said 87 percent of the F-35 software was already in use on F-35 jets that were flying, and 9.1 million of the 9.4 million lines of code required for the jet had been completed.
Officials reviewing the program also discussed the high costs of maintaining and operating the aircraft, delays in software development, and continuing issues with an internal Lockheed system aimed at tracking the cost of the F-35 program, said the sources, who were not authorized to speak publicly.
The sources said F-35 flight testing was going well, and initial training flights were taking place at Eglin Air Force Base, but Pentagon officials are increasingly frustrated that the technology issues were taking so long to resolve.
“More progress is needed on the complex development activity,” said one of the sources. “There’s frustration that it’s not happening fast enough.”