THE LITTLE LAGOON at Pershing Park has been filled, the artificial waterfall is falling, and a large population of pink geraniums is in full chorus. The lunch stand is doing a land-office business on sunny days, and you have to get there early for a table. Otherwise, you sit on the stone steps, looking at the reflection of the young birches in the water. Pershing Park -- the block along Pennsylvania Avenue, between 14th and 15th streets NW -- was opened formally a few days ago, adding another welcome touch of color and civility to downtown Washington.

That block used to be Pershing Square, a plot of grass and well-tended flower beds. It's now bigger, more elaborate and a more inviting place to sit. The cityscape never comes cheap. The cost, together with its companion Western Plaza and the work on the surrounding streets and sidewalks, has been about $25 million. Perhaps it can be justified; that spot is, after all, the main crossroads of the capital. But it's probably just as well that the work was almost finished before the present tenant moved into the White House a block away.

Western Plaza, on the other side of 14th Street in front of the District Building, is the open area with the L'Enfant plan for the city laid into its paving. In contrast to Pershing Park, it's mercilessly unshaded and, at least to our eye, a bit bleak. The designers' idea, according to the Pennsylvania Avenue Development Commission, which presided over the whole complex, was to preserve the vista of the Capitol unobstructed and to provide a place for civic celebrations. Drums, bugles, Boy Scouts and that sort of thing -- under the cool professional gaze of Gen. Pulaski, sitting on his horse over by 13th Street.

There are no horses and no statues in Pershing Park. But you will find incised in one wall two military maps of the area above Paris in the summer of 1918, and a brief explanation. As you read, remember that it is a description, in the desiccated prose of official history, of the final episode of the central deforming catastrophe of this century. Those maps in the stone refer to the fields and valleys where some 115,000 Americans died in those six months of 1918 -- a terrible toll, and yet the American casualties in that way were little more than one-tenth Great Britain's battlefield deaths, and Britain's losses were fewer than France's or, especially, Germany's or Russia's. Some 10 million men were killed in that war.

Pershing Park is a sweet little enclave in the city, shining under a spring sun. It's a peaceful spot, and yet the inscription on the wall there will remind you of the price of peace, and the cost of failing to keep it. The sight of children in the park brings to mind the generation of children born around, say, 1895, which was a year of general peace and stability. This line of thought is not an entirely comfortable one, but it's worth pursuing for a moment if you have the time this Memorial Day weekend.