Federal officials gave the go ahead Thursday on the design plan for a spy campus in Bethesda despite residents’ concerns about a proposed parking garage that could block their view of the Potomac River and the historic C&O Canal. The six-story garage, just one facet of a 3,000-employee “Intelligence Community Campus” that will replace the former headquarters of the National Geospatial Intelligence Agency on the Potomac, is expected to eliminate almost an acre of existing woodland in the exclusive Palisades community nearby. Residents also argue the structure will block their view of the river.