WASHINGTON (Reuters) - Auto executives headed to Capitol Hill for a second day to argue their case for a $25 billion aid package in the face of mounting political opposition to another huge government bailout.

The Wednesday hearings are slated to start at about 10 a.m. before the House Financial Services Committee.

In Senate hearings on Tuesday, Rick Wagoner, the head of General Motors Corp, made it very clear that the executives felt compelled to appear before Congress this week.

"This is about much more than just Detroit," Wagoner said in his testimony. "It's about saving the U.S. economy from a catastrophic collapse."

The weakened economy and global credit crisis pushed the U.S. government into bailing out companies including insurer American International Group Inc, investment bank Bear Stearns, and mortgage companies Fannie Mae and Freddie Mac.

Scheduled to testify on Wednesday are Wagoner; Robert Nardelli, head of Chrysler LLC; Alan Mulally, CEO of Ford Motor Co; Ron Gettelfinger, head of the United Auto Workers union; Annette Sykora, chairman of the National Automobile Dealers Association; James McElya, CEO of Cooper-Standard Automotive Inc; Jeffrey Sachs, professor at Columbia University, and Matthew Slaughter, professor at Dartmouth's Tuck School of Business.

The auto executives were expected to repeat much of what they said on Tuesday when, for the first time, they confirmed how much they are asking from the government. General Motors is seeking between $10 billion and $12 billion, Ford is seeking roughly $8 billion and Chrysler would get $7 billion.