Obama: Long Primary OK As Long As Candidates Watch What They Say

From CBS News' Maria Gavrilovic:

JOHNSTOWN, PA. -- Barack Obama predicted that the lengthy primary will not divide the Democratic party only if he and Hillary Clinton remain measured in their criticisms of each other.

"I do want to make sure, to the extent that I can control it, that we show some restraint and we are measured in how we present the contrast between myself and Senator Clinton," Obama said at a press conference here.

"We've been very careful throughout this campaign not to say things that could be used as ammunition for the Republicans if Senator Clinton were the nominee."

Obama admitted that his surrogates and those of Clinton are not "blameless" in their attacks on each other. He said that calls from his supporters, such Sen. Patrick Leahy, D-Vt., for Clinton's withdrawal from the race stem from "irritation." However he argued that the high voter turnout in primaries and caucuses will bode well for the Democratic Party.

Obama said he expects to do well in the Pennsylvania primary; however, he described himself as the underdog in the race and stopped shy of predicting a win.

"I'm not as well known as Senator Clinton is in this state which is reflected in the polls, and she's got a popular Democratic governor that gave her a good head start, and provided her with some institutional support," Obama said, referring to Gov. Ed Rendell, D-Pa.

"We want to do as well in Pennsylvania. We may not be able to win but I think we've got a good chance and we're going to work as hard as we can."

Sen. Bob Casey, D-Pa., who has been campaigning with Obama, said he will have difficulties competing against Clinton in the state.

"Look at the other side, they've been campaigning in the state for fifteen years," Casey said.

"So it's a tall order but we're making progress."