Tetra Tech Inc. on Wednesday said that the Defense Department’s Missile Defense Agency awarded it a $270 million contract for advisory services related to development of a ballistic missile defense system for the United States.

The Pasadena engineering consulting company said it is one of three firms to receive five-year contracts. Tetra Tech has worked as a prime contractor for the Pentagon’s missile agency since 1998. The work for the Missile Defense Agency Engineering and Support Services contract will be performed primarily in Huntsville, Ala.

Shares were down 9 cents, or less than 1 percent, to $20.32 in midday trading on the Nasdaq.