Tetra Tech Inc. said Tuesday that it has acquired the assets of DPK Consulting, a firm with approximately $15 million in annual revenue that provides consulting services for the U.S. Agency for International Development.

The Pasadena-based provider of consulting, engineering, and technical services said DPF, which has about 120 employees worldwide, helps developing and transitioning governments improve regulations and the rule of law. Other clients of the San Francisco firm include the World Bank, Asian Development Bank, and a variety of foreign governments.

Terms of the acquisition were not disclosed.

“By acquiring DPK, Tetra Tech is taking another important step toward rounding out our full-service offerings to USAID, which has become one of Tetra Tech’s largest customers,” said Chief Executive Dan Batrack in a statement.

Tetra Tech also announced that it is one of five contractors to share a new five-year, $500 million contract for the USAID. The company will provide engineering studies and design services for USAID-funded infrastructure projects worldwide, including water resources, civil infrastructure, telecommunications and power generation programs. Much of the work will be performed in areas recently affected by disaster or conflict.

Separately, the company said it was awarded new work by the ports of Los Angeles and Long Beach to assist with the ports’ Clean Trucks Program and related green projects. The contract will be worth $25.6 million over the next five years.

The trucks program, which launched Oct. 1, is designed to reduce truck air pollution at the ports 80 percent by 2012. Tetra Tech, which has provided environmental and coastal engineering services at the ports for more than 15 years, now will support the program’s truck fleet modernization component.

Tetra Tech shares were down 12 cents, or 1 percent, to $18.65 in morning trading on the Nasdaq.