|Serving a summons and complaint on the USA is a two or three-step process.
Step 1: Deliver a copy of the summons and of the complaint to the United States attorney for the district where the action is brought—or to an assistant United States attorney or clerical employee whom the United States attorney designates in a writing filed with the court clerk—or send a copy of each by registered or certified mail to the civil-process clerk at the United States attorney’s office. Note: The US Attorney is generally located within the USDC courthouse in each district.
Step 2: Send a copy of each by registered or certified mail to the Attorney General of the United States at Washington, D.C. Note: U.S. Department of Justice is located at 950 Pennsylvania Avenue, NW, Washington, DC 20530-0001.
Step 3 (when applicable): If the action challenges an order of a nonparty agency or officer of the United States, send a copy of each by registered or certified mail to the agency or officer.
For more information, refer to the Federal Rules of Civil Procedure here.