ANTIETAM, the battle that ought to have brought the Civil War to an earlier end, will be commemorated this weekend in tours and talks and song and ceremony on the battlefield where more than 20,000 men fell on the bloodiest day of the war, 125 years ago this week.

Hundreds of authentically uniformed volunteers will demonstrate and act out various facets and phases of the battle, in which Union commander George B. McLellan -- who had Robert E. Lee's plans in his hands -- spilled the blood of his troops like water, yet failed to make the one last push that could have trapped Lee and his whole army on the northern bank of the Potomac. Although torn to tatters, the Southern army slipped away to fight again another day.

Friday, four half-hour tours between 10 and 4 will go over the ground, recalling the morning, midday and afternoon phases of the battle and the awful aftermath.

From 6 to 7 there will be a Civil War songfest at the Antietam National Battlefield visitor center, followed by a lecture on the "Debacle in the West Woods," the cruelest episode of that cruelest day: More than two thousand men were mowed down in minutes.

Saturday the center opens at 8 and the day will be filled with demonstrations of weapons and tactics. The Confederate camp will open to visitors at 10 and the Union camp at 3; the uniforms, weapons, gear and tents of these latter-day warriors are often museum-quality reproductions. From noon to 1 artillery will echo over the fields of this least-changed of all major Civil War battlefields, followed by a parade along Sharpsburg's Main Street.

At 6 will come a performance at the visitor center of "Glory Road," an original folk-music suite commemorating the battle. From 7 to 10 (yes) there will be a torchlight tour, "War Comes to Washington County," starting from the visitor center and appropriately punctuated with vignettes related by park personnel and volunteers.

Sunday the camps will open at 8:30 and at 10 there will be a nondenominational service at the Dunker Church, a modest house of worship around which the slaughter raged in 1862. Tours and demonstrations through the day will be capped by closing ceremonies, beginning at 2:30 with a U.S. Army concert, "Voices from Antietam." TO GET THERE --

Antietam National Battlefield is about 60 miles from Washington. From the Beltway take I-270 north to Frederick and I-70 west to Alternate U.S. 40 west. At Boonsboro take Rte. 34 south to Sharpsburg.