Last March, the federal government set up a Web site to make public a vast archive of Iraqi documents captured during the war. The Bush administration did so under pressure from Congressional Republicans who said they hoped to “leverage the Internet” to find new evidence of the prewar dangers posed by Saddam Hussein. But in recent weeks, the site has posted some documents that weapons experts say are a danger themselves: detailed accounts of Iraq’s secret nuclear research before the 1991 Persian Gulf war. The documents, the experts say, constitute a basic guide to building an atom bomb. Last night,...