Greenbelt, city (1990 pop. 21,096), Prince Georges co., W central Md., a residential suburb of Washington, D.C.; chartered 1937. Greenbelt was planned and built by the federal government as an experimental model community for families of modest income. The huge National Agricultural Research Center borders the city on two sides, and the NASA Goddard Space Flight Center is nearby. The National Park Service maintains Greenbelt Park in the city (see National Parks and Monuments, table).