For a Battered Populace, a Day of Civic Passion
Scene at Baghdad polling station is suffused with sense of civic spirit, dispelling suspicion that 24 years of bludgeoning under Saddam Hussein had bred disabling passivity among country's 28 million people; voters walk long distances through streets choked with military checkpoints, and stand for hours in line to cast their ballots; these are same people who crowded polling centers in 2002 to re-elect Hussein in one-candidate referendum by official vote count of 100 percent; after surprise of heavy turnout on Jan 30, there is much that remains to daunt American hopes that Iraqis would come together in new political compact, one that would enable their new national assembly to draft constitution, submit it to referendum, and hold another election late this year for full-term parliament and government; Americans who have remained decisive authority in Iraq emerge from voting with large measure of vindication for having pressed ahead with election despite predictions that enterprise would collapse amid uncontrollable insurgent violence or crippling voter boycott; photos (M)