Runners zagged around it, pedestrians stepped over it and children stared and tugged at their mothers' hands to get a closer look at it. It was a large pile of five-day-old horse droppings languishing on the sidewalk outside the Smithsonian's American History Museum.

Elaine Hillard, who works at the Agriculture Department, is the one who sounded the alarm. After 30 years of traipsing across the Mall, she knew what she saw was not proper.

"I am proud of my nation's capital," she said. "I'd like everyone to have pride in their city. And that is an affront to anyone."

Hillard said she called the office of Mayor Marion Barry Wednesday and was assured the mess would be cleaned up, but it was still there yesterday, in the middle of the sidewalk on 12th Street NW between Constitution Avenue and Madison Drive.

That part of 12th Street, however, is federal property and the villain appears to be a horse belonging to the U.S. Park Police mounted unit that regularly patrols the Mall.

Sgt. Paul Johnson, who heads the 12-horse unit, said this was the first complaint he had received.

"Horse defecation is biodegradable and usually will wash away or disintergrate within three to four days," he said, noting that horses usually prefer grassy areas to concrete sidewalks.

Johnson said horse-mounted officers often write tickets along 12th Street because it is permit-only parking area and there are frequent violators. "The officer may have written a lot of tickets and the horse just couldn't wait," he theorized.

Johnson takes complaints seriously: "We'll clean it up. I will personally see to it."