The U.S. Office of Personnel Management coordinates hiring for the federal government and uses the official General Schedule, or GS, to describe positions and announce job openings. The federal government employs more than 2 million people in civil service and is the nation's largest employer. GS jobs generally offer competitive salaries and benefits and good job security. However, very few federal jobs are available to resident aliens.
Executive Order 11935
The White House issued Executive Order 11935 in 1976, "Citizenship Requirements for Federal Employment," which requires federal agencies to hire United States citizens for almost all civil service GS positions. Although the order has been amended numerous times since 1976, the basic restriction still remains intact.
There are other legal restrictions on hiring non-citizens, including immigration law and annual Congressional appropriations that prohibit most cases of spending federal dollars to hire non-citizens.
In very limited circumstances, agencies can hire resident aliens or other non-citizens. In general, such hiring is limited to instances where a job would be very difficult or even impossible to fill from the domestic workforce of U.S. citizens. For example, a job may call for knowledge of an obscure language or foreign customs for which an agency has not identified an eligible U.S. citizen.
Federal GS jobs are listed at the official USAJOBS.gov website. You can use the keyword search tool at the site to search on the term "non-citizens" to identify jobs that contain this term and which may be available to resident aliens. Note that some jobs contain phrases like "non-citizens are not eligible" and will be returned in a USAJOBS search, even though the position is not open to resident aliens.