WASHINGTON — Lockheed Martin Space Systems and Raytheon Co. will join forces to compete for a massive contract to operate and continue development of the United States’ primary strategic missile shield, the companies announced Aug. 5.

The U.S. Missile Defense Agency (MDA) in the coming weeks is expected to release the final request for proposals for the job of managing all operations, maintenance and modernization for the Ground-based Midcourse Defense (GMD) system. Award of a single prime contract worth about $600 million per year is anticipated in early 2011.

Sunnyvale, Calif.-based Lockheed Martin and Waltham, Mass.-based Raytheon hope to unseat current GMD prime contractor Boeing Defense, Space & Security of St. Louis, which announced in June it would team with Northrop Grumman Corp. for the competition. Boeing has been responsible for the development, operations and sustainment of the GMD system since its inception in 1998.

The Lockheed Martin-Raytheon team will be based in Huntsville, Ala., Mat Joyce, Lockheed Martin’s GMD vice president and program manager, said during a conference call with reporters. Raytheon currently provides the exo-atmospheric kill vehicle for the GMD interceptors located in Alaska and California, and the two companies have previously worked together on the Patriot, Aegis Ballistic Missile Defense and Terminal High Altitude Area Defense systems, Joyce said.