April 20 (Bloomberg) -- New York Senator Charles Schumer predicted Democratic presidential candidate Hillary Clinton will have a ``significant'' win in Tuesday's Pennsylvania primary.

``My guess is she will win Pennsylvania by a significant margin,'' Schumer, a Clinton supporter, said today on ``Fox News Sunday.'' He declined to predict the margin of victory.

Clinton is holding on to a lead in Pennsylvania, according to an April 17-19 American Research Group survey that had her leading Illinois Senator Barack Obama 54 percent to 41 percent. Clinton is counting on a win in Pennsylvania to narrow Obama's lead in delegates for the Democratic nomination.

Clinton trails Obama in the number of Democratic delegates, who will select the party nominee in August. An unofficial tally by the Associated Press shows Obama with 1,645 to Clinton's 1,507. A candidate needs at least 2,025 to win.

Pennsylvania has 158 pledged delegates at stake, awarded proportionally based on the popular vote in congressional districts and statewide.

Illinois Senator Richard Durbin, an Obama backer, said Clinton faces considerable challenges in overcoming Obama's delegate lead because of the shrinking number of states holding contests. After Pennsylvania, voters will go to the polls in North Carolina and Indiana on May 6.

`Math Is Unforgiving'

``The math is very unforgiving at this point when it comes to delegate counts,'' Durbin said. ``The Clinton campaign is running out of real estate.''

A Bloomberg/Los Angeles Times poll conducted April 10-13 showed Clinton leading Obama by 5 percentage points in Pennsylvania. In Indiana, Obama led by 5 points, and in North Carolina, he held a larger, 13-point advantage. The poll of likely Democratic voters had a margin of error of plus or minus 4 percentage points.

If the two contenders trade narrow victories in Pennsylvania and Indiana while Obama wins decisively in North Carolina, that almost certainly would add to his delegate majority and, with only seven primaries left, make it almost impossible for Clinton to catch up.

Schumer predicted that after Pennsylvania, a Clinton win in Indiana would give her ``momentum.''

``Barack Obama has had several chances to put it away. He hasn't,'' Schumer said. ``It's very close.''

Rendell's Prediction

Pennsylvania Governor Ed Rendell, speaking later on CBS's ``Face the Nation,'' said Clinton would win the state by as many as seven percentage points, even in the face of ``obscene'' campaign spending by Obama in the days leading up to the vote.

``We've been outspent three-and-a-half to one,'' Rendell, a Clinton supporter said. ``A win by middle-digits -- four, five, six, seven -- would be very significant.''

The state's democratic senator, Obama supporter Bob Casey, said Obama has campaigned heavily in the state and closed what was initially a wide gap between the two candidates.

``He's made tremendous progress in the last six or seven weeks,'' Casey said. ``I don't know if it's enough progress to have a close race or a winning race.''

Casey predicted that the nomination would be decided before Democrats hold their convention in Denver in August; Rendell cautioned that there is still a long way to go.

Race May Continue

``It really depends on what happens in the next nine states,'' Rendell said. ``There's a chance it could be over by the convention, but there's a chance it could go to the convention.''

Appearing on NBC's ``Meet the Press,'' Clinton chief strategist Geoff Garin said the process must be given time to ``play through.''

``We'll see where we are on June 3,'' Garin said, referring to the date of the final Democratic nominating contests, in Montana and South Dakota. ``There's no need to make a rush to judgment here.''

Jon Corzine, the Democratic governor of New Jersey and a superdelegate who supports Clinton, said voters are ultimately going to have to support whoever they think has the best chance to beat John McCain, the presumptive Republican nominee.

``Superdelegates ought to wait until June, see how the primaries run out, make a decision about who is going to be the most electable,'' Corzine said on CNN's ``Late Edition.''

`Better Than Bush'

Campaigning today in Reading, Pennsylvania, Obama said McCain would be an improvement over the current Republican administration.

``You have a real choice in this election,'' Obama told a town hall gathering. ``Either Democrat would be better than John McCain. And all three of us would be better than George Bush.''

McCain today called on Obama to condemn stances held by William Ayers, a former member of the radical group the Weather Underground, who gave money to Obama's Senate campaign.

The Weather Underground carried out a series of bombings in the early 1970s -- including the U.S. Capitol and the Pentagon. While Ayers was never prosecuted for those attacks, he told the New York Times in an interview published Sept. 11, 2001, that ``I don't regret setting bombs.''

``How can you countenance someone who was engaged in bombings which could have or did kill innocent people?'' McCain said today on ABC's ``This Week'' program.

In the April 16 Democratic debate, Illinois Senator Obama compared his relationship with Ayers to his friendship with Republican Senator Tom Coburn, who Obama cited as once saying that the death penalty might be appropriate for those who administer abortions.

McCain today called the comparison with Coburn, a physician, ``the worst thing of all.''

To contact the reporters on this story: Nicholas Johnston in Washington at njohnston3@bloomberg.net.

Last Updated: April 20, 2008 15:49 EDT