They are ruining Washington, ruining it in the name of saving it.

Five years after the Sept. 11 terrorist attacks, this once-lovely city of broad diagonal avenues and open vistas conceived in 1791 by French engineer Pierre L'Enfant is becoming an ever more-militarized zone that illustrates the profound tensions roiling throughout government buildings around the nation. Playing out in big cities such as Chicago as well as small ones such as Peoria, that tension is between security and openness, the imperative to fortify and the desire to beautify.

And in this struggle between armor and aesthetics, armor is invariably emerging the victor, marring public buildings and public spaces that symbolize the highest ideals of democracy and help hold together a diverse, often-fractious society.

Capitol Hill is a zone of fear, welcoming the tourists with fences, slanted concrete barriers, steel walls that pop out of the pavement and steel posts called bollards that are designed to hold a vehicle-delivered bomb at bay. The bollards trample the picturesque grounds of the great landscape architect Frederick Law Olmsted, like the battalion of Mickey Mouse's endlessly multiplying brooms in the movie "Fantasia."

The sidewalks of the Federal Triangle, that wedge of lordly classical office buildings between the Capitol and the White House, are cluttered by an ever-expanding assortment of fat planter pots and closely spaced steel and concrete bollards. Despite their clumsiness, no bureaucracy can resist them.

The two-block stretch of Pennsylvania Avenue in front of the White House, which then-President Bill Clinton closed to traffic after the Oklahoma City bombing in 1995, has been transformed into a bland pedestrian mall, a soulless precinct that drums out vitality from the cityscape.

To visit here now is to realize that America has entered a new phase, in which various arms of the federal government have started replacing the temporary security measures installed in the aftermath of Oklahoma City and Sept. 11 with permanent ones.

Yet these designs, while less obviously ugly than their makeshift predecessors, are visually monotonous, functionally one-dimensional, insensitive to treasured landscapes and debilitating to city life. And they are costing taxpayers big-time, not just in the modern-day equivalents of medieval walls and moats but in the beefed-up structures of the federal buildings themselves.

Since a yellow Ryder truck driven by Timothy McVeigh exploded outside the Alfred P. Murrah Federal Building in 1995, killing 168 people and injuring 850, the federal government has spent at least $1.2 billion on protection against a vehicle-delivered bomb, according to "Security Planning and Design," a primer for designers introduced in 2004 by the American Institute of Architects.

Officials at the General Services Administration, the federal agency that erects, manages and leases federal buildings in 500 cities nationwide, declined to comment on that figure. But David Winstead, the GSA's commissioner of public buildings service, acknowledged that the cost of surrounding one city block with bollards and other perimeter security measures is about $1 million. A single bollard, secured in a concrete foundation, costs $5,000 to $8,000 apiece, according to interviews with designers and planners.

Then there are the intangible costs, which go beyond ugliness to the locked doors and closed streets that restrict movement or hinder citizens' ability to have direct contact with those who govern them. When the overriding purpose of government buildings becomes warding off danger, these structures invariably lose the chance to become centers of community or to communicate traditional American values of openness and optimism. Instead of government buildings that open their arms to welcome us, as Helmut Jahn's James R. Thompson Center in Chicago does with the tiers of curving exterior glass, which invite passersby into its soaring atrium, we get buildings that elbow us away.

America the Beautiful becomes America the Besieged.

If you doubt that, look at the temple of the Treasury Department, ringed by a fence and a guard house, and greeing you with this sweet sign: "Passholders and Appointments ONLY." If this is how we're going to treat federal buildings, then why not simply move them, like the Vice President, to an undisclosed location?

The bunker mentality is bipartisan, however, so the self-inflicted damage is hardly confined to Washington.

The self-inflicted damaged, though, is hardly confined to Washington.

In Chicago, it ranges from the Chicago Federal Center in the South Loop, where tombstonelike granite posts disturb the minimalist openness of the complex of matte-black high-rises designed by Ludwig Mies van der Rohe, to an FBI building that opens Tuesday on the city's West Side. It is surrounded by the mother of all fences, a generic, government-issue barrier of metal and concrete close to 6 feet tall that stretches endlessly along Roosevelt Road.

In St. Louis, over the objections of local architects who fought for a more creative solution, graceless steel bollards surround Eero Saarinen's glistening, gracefully soaring Gateway Arch, which at 630 feet is the nation's tallest monument. A Humvee blocks a sidewalk leading to the Arch from downtown St. Louis. Even small cities cannot escape the scourge. Peoria's federal courthouse, a classical gem whose walls are adorned with lovely sculptures, is now ringed by stumpy concrete bollards that are completely unsympathetic to its design.

Yes, the nation is fighting a war on terrorism, a war that struck directly here on Sept. 11 when terrorists crashed a hijacked jet into the west wall of the Pentagon, killing 184 people. And the dangers of that war remain clear and present, as underscored by last month's revelation of a terrorist plot to use liquid explosives to blow up several trans-Atlantic airliners. It would be foolish to do nothing.

But what is happening in Washington and other concentrations of federal power raises vexing questions, to which there are no simple answers.