A behind-the-scenes battle broke out late Tuesday over superdelegates who had secretly committed to Sen. Barack Obama (D-Ill.), with Clinton campaign officials scrambling to “freeze” them before they announced support for him.

The battle reflects the trench warfare that both campaigns expect if the battle for the Democratic presidential nomination stretches on to the Pennsylvania primary on April 22.

Democratic officials involved in the conversations said Obama was lining up a package of superdelegates — the party insiders whose votes help select the Democratic nominee — with plans to announce their support as a bloc.

Obama also plans to announce he raised more than $50 million in February, considerably more than Clinton’s $35 million.

The Obama theory was that the separate announcements would convey juggernaut-like momentum if Obama had big wins on Tuesday, and would help turn the page if he had a disappointing showing in the Texas or Ohio primaries.

But aides to Sen. Hillary Rodham Clinton (D-N.Y.) became convinced by network exit polls and her own data that she would have a stronger-than-expected showing. So they immediately began urging Obama’s prospective superdelegates to withhold their support.

An Obama aide said: "Despite last-minute Clinton pranks, the rumor they're floating about a massive superdelegate rollout tomorrow is not true."

One Democratic lawmaker described “pushback” from the Clinton campaign but did not elaborate.

A senior Clinton aide said her supporters were scrambling to "freeze" members of Congress on the verge of announcing for Obama, and said a good night for Clinton would be key to forestalling the move.

The Obama campaign had an extensive “whip” organization set up to track and woo these officials, including members of Congress.

“We’ll wake up tomorrow and we’ll see where folks are,” an Obama aide said. “We have new support every single day.”

Obama forces responded to the Clinton overtures by telling superdelegates that regardless of Tuesday’s outcome, Obama would retain the lead in elected delegates.

An Obama official said his campaign plans to argue that even if she scored one or more victories on Tuesday, it would be “virtually impossible” for her to catch up in the delegate count.

An Obama statement said: “Three weeks ago, when they led polls in Texas and Ohio by 20 points, the Clinton campaign set their own test for today's primaries. They confidently predicted that they would win by landslide margins and wipe out the substantial edge Barack Obama has built in pledged delegates.

“But what we've seen is that voters in Ohio, Texas, Vermont and Rhode Island share the same urgent desire for change we have seen throughout the country. That's why we're confident that Barack Obama will maintain his delegate lead, leaving the Clinton campaign to explain why they failed their own test and exactly how they plan to win a nomination that, after tonight, will be virtually out of reach.”