Many agencies within the U.S. government deal with the topics of art, architecture, and engineering. To see how the Federal government is structured and for a summary of what any particular agency does, you can look at the U.S. Government Manual.
You can find information about jobs (and salaries) in art, architecture, and engineering in the Occupational Outlook Handbook .
U.S. Forest Service Department of Defense Farm Security Admin. General Services Admin.
Library of Congress - Historic American Buildings Survey