Democratic Party presidential contenders Senators Hillary Clinton and Barack Obama are campaigning across the northeastern U.S. state of Pennsylvania in an effort to win every last vote before Tuesday's key nominating contest.

The rivals exchanged attacks during their multi-stop runs across the state Saturday. Clinton said Obama offered more flash than substance. Obama attacked both Clinton and Republican presidential candidate John McCain. He said Clinton would not change how business is done in Washington. And Obama said McCain would just continue the policies of the Bush Administration.

Clinton currently leads Obama in opinion polls in the state, although her margin over him has narrowed recently. She needs a convincing win in Pennsylvania to keep open her chance of winning the White House in November.

Obama leads Clinton nationally in the number of pledged delegates who will select the Democratic nominee at the party's convention in August.

On Friday, Obama's campaign announced the Illinois senator is being endorsed by former Senators Sam Nunn and David Boren. Robert Reich, who served as labor secretary in the Clinton administration, is also backing Obama.

Some information for this report provided by AP and AFP.