If the date April 3, 1974 means nothing to you, it's a cinch you weren't in Xenia, Ohio on that quiet Wednesdy afternoon when a low-pressure system from Wyoming collided with a mass of warm, humid air from the Gulf of Mexico. There were tornadoes from Texas to the Great Lakes that day, but the news apparently reached only a handful of Xenians. Spinning at several hundred miles an hour, a huge partial vacuum passed over the little town, exploding windows, pulling nails out of walls, sucking up trees, ripping steel girders. Laffoon, a Cincinnati newspaper reporter, has put together a painstaking documentary which concentrates chiefly on the aftermath of the storm--the impromptu hospital arrangements, the arrival of organizers from HUD and the Federal Disaster Assistance Administration, the efforts of the Red Cross and the remarkable Mennonite Disaster Services, the controversial business of appraising damage and scheduling the remains of buildings for demolition or salvage. There was much bad feeling about rebuilding priorities; there were inevitable blunders. Laffoon doesn't gloss over the ugly spots, but he also does justice to the incredible variety of human coping: young Picky Fallis carrying his dead fiancee's picture all summer before falling in love with another girl, the Mallow brothers calmly planting the site of their devastated orchard with summer crops after the builders of their barn heroically made good on a replacement guarantee, Jackie Hupman taking heart as the cat unexpectedly emerges from the ruins of her house. Despite a certain paste-and-scissors effect inevitable in this sort of reportage, Laffoon solidly conveys both the tangibles and the intangibles of a complex event whose full bitterness, we realize at the end, has yet to be felt.