(Adds response from losing bidder)

By Andrea Shalal

WASHINGTON, Jan 14 (Reuters) - Northrop Grumman Corp beat out Boeing Co to win a contract worth up to $963.5 million to maintain the U.S. stockpile of intercontinental ballistic missiles, the Pentagon announced on Wednesday.

The contract marks a big win for Northrop Grumman over Boeing, which built the Minuteman missile systems and had competed for the support contract.

Boeing said it was disappointed by the U.S. Air Force's decision and would decide whether to protest the contract award after a full briefing by the Air Force.

"We have requested a debrief and will determine a path forward following completion of the debrief," said Boeing spokeswoman Queena Jones, when asked if Boeing could file a protest against the contract.

"We believe Boeing provided the best solution to sustain the Minuteman ICBM program, leveraging Boeing's 55 years of experience in ICBM development and maximizing the benefits of Boeing's personnel, capabilities, and original equipment manufacturer expertise," Jones said.

The contract, which runs through Jan. 31, 2020, covers sustainment engineering, technical assistance and program management services for ground subsystems associated with the missiles at a wide range of U.S. Air Force bases, the Defense Department said.

(Reporting by Andrea Shalal; Editing by Chris Reese and Lisa Shumaker)