Defense Undersecretary Frank Kendall said he still hoped Raytheon could get the long-delayed program under control since it was critically needed.

"It would be very disruptive to stop where we are and start over," Kendall said, adding that he expected to continue carrying out high-level quarterly reviews.

He said Raytheon was putting additional resources into the program, and he still believed that Raytheon could resolve the issues and deliver the system.

But he said it was critical that the company continued to improve its performance.

His biggest concern now, Kendall said, was that the U.S. Congress could cut funding for the program and make it difficult to execute the work needed now.

The Pentagon earlier this year said the estimated cost of Raytheon's Operational Control System (OCX) rose 16.3 percent, or $586.4 million, to $4.2 billion in 2015 - even before a two-year delay decision that will inflate costs further.

The cost was estimated at $1.5 billion when Raytheon won the contract in 2010.

(Reporting by Andrea Shalal)