Iowa Straw Poll Proving a Little Can Mean a Lot
Nine Republican Presidential candidates scour state of Iowa in advance of straw poll at Iowa State University; poll has never in last 20 years accurately predicted Presidential victor, but because primary season has begun far earlier than usual, straw poll could supplant Iowa caucuses in weeding out 10-candidate field; contenders themselves have raised stakes, and expectations, by elevating importance of event; even campaigns that are struggling are portraying event as crucial test of campaign's organizational mettle; those hoping to make impressive showing include former Vice Pres Dan Quayle, Patrick Buchanan, former Gov Lamar Alexander, Sen Orrin Hatch, Alan Keyes, Steve Forbes, Elizabeth Dole, Gary Bauer and front-runner, Gov George W Bush; only Sen John McCain is bypassing event; photo (M)