Tetra Tech Inc. has signed a definitive agreement to acquire the State Department consulting firm PRO-telligent LLC.

The Pasadena engineering and technical support firm said that PRO-telligent of Arlington, Va. provides a wide range of security and intelligence-oriented technical support services, mostly for State Department outposts around the world. It employs more than 600 people and has annual revenue of about $100 million.

The State Department’s U.S. Agency for International Development is an important Tetra Tech client. The deal “complements our strategy to better serve our customer, a long-term goal we’ve expressed for several years,” Chief Executive Dan Batrack said in a prepared statement.

PRO-telligent will join Tetra Tech’s Technical Support Services group. Financial terms were not disclosed.

Tetra Tech shares were up 19 cents, or less than 1 percent, to $19.36 in midday trading on the Nasdaq.