Edwards Challenges Kerry Over Who Can Win
Democratic candidates hold lively 90-minute debate as they head toward biggest day of primary voting in Democratic nomination battle; Sens John Kerry and John Edwards clash over who has greater ability to woo independent voters and defeat Pres Bush; under persistent questioning from CNN and Los Angeles Times panel, both express their opposition to gay marraige and to Pres Bush's call for constitutional amendment to bar it; Kerry is also challenged on his opposition to death penalty, position that Democrats have long feared could cause him problem; debate also includes Rep Dennis J Kucinich and Rev Al Sharpton; photo (M)

