ALBANY — State environmental officials took action on Friday to hold the federal Defense Department accountable for water contamination in Newburgh, N.Y., saying that firefighting foam containing a dangerous chemical, used at a local military base, polluted the city’s water supply.

The New York State Department of Environmental Conservation declared Stewart Air National Guard Base, home to the 105th Airlift Wing of the New York Air National Guard, a state Superfund site.

According to the state agency, the base for years used a type of foam for aircraft emergencies and training purposes that contained PFOS, or perfluorooctanesulfonic acid, which has been linked to cancer and other medical problems. The chemical — no longer used at the site — then polluted a tributary leading to Lake Washington, the primary source of Newburgh’s drinking water, the department said.

State officials began to focus on the problem in Newburgh earlier this year, after another water scare shook Hoosick Falls, N.Y., a village near the Vermont-New York border, about 30 miles northeast of Albany.