U.S. Says Lockheed Must Pay Part of F-35 Cost Overruns

The official, Ashton B. Carter, an under secretary of defense, said he had delivered that message to the company’s chief executive, Robert J. Stevens, on Sunday at a meeting on how to get the program back on track.

The meeting was prompted by an internal Pentagon report suggesting that work on the new stealth fighter, the Pentagon’s largest weapons program, had fallen so far behind that it could cost $16.6 billion more than expected over the next few years.

Dr. Carter told reporters that the Pentagon might add more planes to the flight test program and encourage the company to hire more software engineers to finish the planes faster.

Lockheed Martin has described the latest Pentagon cost estimates as a worst case. It has said it is making manufacturing improvements that could keep the costs from ballooning and help it get back on schedule by 2011.

Dr. Carter said he wanted to make changes now to bolster the program, which could cost $300 billion for more than 2,400 planes, to be bought over 25 years.