CLINTON, Iowa  On the final weekend before Iowa’s presidential caucuses, the Democratic contenders tangled over electability Saturday as the leading Republican candidates delivered fresh attacks on their rivals, hoping to nudge undecided voters to reach a decision in an extraordinarily volatile campaign.

“Who is tested and ready to be the winning candidate for the Democratic Party?” said Senator Hillary Rodham Clinton of New York, arguing her ability to fend off Republicans. “They’ve been after me for 16 years. And much to their dismay, I’m still here.”

Senator Barack Obama of Illinois took the rare step of mentioning his leading rivals by name. He pointedly told voters he believed that Mrs. Clinton would “start off with half the country not wanting to vote for her.”

Image Mitt Romney speaking in Altoona, Iowa, on Saturday. Credit... Beatrice de Gea for The New York Times

Asked about Mr. Obama’s comments, Mrs. Clinton named Democrats supporting her, including Gov. Ted Strickland of Ohio, who traveled with her Saturday. “They are not on a political suicide mission,” she said.