WASHINGTON — Sen. John McCain's prospect for winning Super Tuesday has received a major boost with the departure of Rudy Giuliani from the Republican presidential field, but the impact of former Sen. John Edwards' suspension of his Democratic campaign is more complex.

Following his poor showing in Florida, Giuliani endorsed McCain at a Wednesday news conference in California, calling him "the most qualified candidate to be the next commander in chief of the United States."

"He is an American hero," Giuliani said. "And America needs heroes in the White House."

California Gov. Arnold Schwarzenegger also will endorse McCain today, according to McCain adviser Steve Schmidt — a boost in the nation's biggest state.

Edwards said at a news conference in the 9th Ward of New Orleans, "It's time for me step aside so that history can blaze its path. We do not know who will take the final steps to 1600 Pennsylvania Avenue, but what we do know is that our Democratic Party will make history."

He was referring to the prospect that Democrats will nominate a woman — Sen. Hillary Rodham Clinton of New York — or a black — Sen. Barack Obama of Illinois — in a presidential race for the first time.

By choosing to suspend his campaign rather than dropping out, Edwards did not release the 56 delegates he has accumulated. He may pick up additional delegates in upcoming primaries.

Edwards said he told Clinton and Obama of his decision.

"They have both pledged to me — and more importantly, through me to America — that they will make ending poverty central to their campaign for the presidency," he said.

He also plans to meet individually with Clinton and Obama in private before deciding whether to make an endorsement or remain neutral.

"Edwards' supporters will be conflicted about where to go," said David Redlawsk, a political scientist at the University of Iowa.

Even if most of voters now supporting Edwards decided to back Obama in upcoming primaries and caucuses, "it's hard to justify that it will be a major catalyst," said David Paleologos, director of the Suffolk University Political Research Center.

"Statistically, Obama will win a few states, but will it be enough going forward?" Paleologos said.

Meanwhile, Giuliani's departure from the GOP field likely will benefit McCain the most in the Northeast next week in states such as Connecticut, Massachusetts, New Jersey and New York, said Dante Scala, an associate professor of political science at the University of New Hampshire-Durham.

"Giuliani's endorsement of McCain only reinforces what voters were likely to do on their own anyway," Scala said.