WASHINGTON, Sept 16 (Reuters) - United Launch Alliance, a joint venture of Boeing Co and Lockheed Martin Corp , has won a contract from the U.S. Air Force for $938 million in additional work on military rocket launch services, the Pentagon said on Tuesday.

The modification of the company's existing contract runs through Sept. 30, 2015, the Defense Department said in its daily digest of major weapons contracts.

The deal will fund additional work in areas such as mission assurance, program management, systems engineering, integration of the space vehicle with the launch vehicle, launch site and range operations, and launch infrastructure maintenance and sustainment, according to the Pentagon.

(Reporting by Andrea Shalal; Editing by Steve Orlofsky)