TEN YEARS AGO, Timothy J. McVeigh and a rental truck filled with 4,000 pounds of fuel-soaked ammonium nitrate, explosives and blasting caps showed what a truck bomb could do to a federal office building filled with workers, visitors and children in Oklahoma City. The nation's capital has never been the same since. Fear of truck bomb attacks, along with post-Sept. 11 security concerns, has changed the face of official Washington, with construction projects blanketing the city from the Capitol grounds to the White House and monuments on the Mall. The latest shrine to come in for permanent security upgrades is the grand structure that, as Thomas Luebke, secretary of the U.S. Commission of Fine Arts, correctly observed in a recent Post article, is "an active forum for the expression of democratic values" -- the Lincoln Memorial. Will the proposed security enhancements at the Lincoln Memorial degrade the majesty and symbolism of a treasured national landmark? That question was prominent for the commission, which gave a nod yesterday to a final protective design but asked its staff to develop additional refinements.

A good deal of the security changes at the Lincoln Memorial are already underway. Road construction around the west side of the memorial is affecting traffic from the Arlington Memorial Bridge and the George Washington Memorial Parkway. Final plans call for the traffic circle to get new pavement and reconfigured lanes to handle a larger morning rush hour. A proposed 30-inch-high, C-shaped granite security wall around the memorial's rear is designed to make the change aesthetically acceptable.

The major point of controversy has been the mouth of the C-shaped wall, which looks east over the Mall toward the Reflecting Pool and the Capitol. Thoughts of placing stone bollards near the top of the memorial's steps or near the base of the bottom step were treated as heresy -- as they should have been. The fine arts commission was asked to approve a concept design that, as The Post's Petula Dvorak reports, places a line of dark metal bollards further away near the Reflecting Pool but far enough from the water for a park maintenance vehicle to pass. Security cables at the outer edges of the staircase leading down from the memorial would be hidden by tall hedges designed to fill gaps between rows of bollards. A final decision by the commission rests on refinements still to be provided.

Terrorism -- or, more precisely, fear of terrorist acts -- has driven the capital of the world's most powerful nation and most open society to this new day of concrete and steel fortifications. The Lincoln Memorial is not immune from the security plan mandated by Congress after the Sept. 11, 2001, attacks, but the memorial is a symbol of our democratic society and must remain open and accessible to the public as a hallmark of freedom.