WASHINGTON — While reforming the government-sponsored enterprises was always going to be a hard battle for the Obama administration, its job will be even tougher if the Republicans, as expected, win control of the House this week.

So far, the only part of Obama's plan that is clear is that he wants to preserve some government guarantee of the mortgage market. But top Republicans on the House Financial Services Committee have already said they oppose that concept.

"It's safe to say we are going to have an ideological showdown if Republicans take the House," said Howard Glaser, a former Department of Housing and Urban Development official who now runs his own consulting firm. "The administration may need to rethink that calculus if Republicans are going to be successful because anything the administration is going to put forward is sure to be viciously attacked by Republicans favoring pristine privatization."

Getting over that threshold question of government support will be difficult, observers said.

"This issue of a government guarantee will be front and center and a big hurdle to overcome," said William Longbrake, the executive in residence at the University of Maryland's Smith School of Business and a former vice chairman at Washington Mutual Inc. "The Republican Party line is they will prefer a private solution."

The administration is required under the Dodd-Frank Act to put forward a plan for the future of housing finance that will include how to deal with Fannie Mae and Freddie Mac, which were taken into conservatorship in September 2008.

While the Treasury Department has remained relatively silent on what it is planning, pledging only to deliver a plan by January, the Republicans have already introduced a bill. The GSE Bailout Elimination and Taxpayer Protection Act would essentially eliminate Fannie and Freddie by gradually phasing out the GSEs' portfolios and increasing their capital.

If the Republicans win this week, the leadership of the House Financial Services Committee appears unclear, but most of the top candidates have signed on to the legislation, including Rep. Spencer Bachus, the chief contender for the job, and Reps. Jeb Hensarling, R-Texas, and Scott Garrett, R-N.J. Most observers said it is likely to be the starting point for the GOP.

"They [Republicans] are more certain what their goals are," said Brian Chappelle, a partner at Potomac Partners. "The theme of the Republicans has been for years to remove the government from the mortgage industry and recent comments by key Republican congressmen continue that mantra. On the Democratic side, the only thing I hear is that they are definitely going to roll out a plan in January. They have been very close to the vest on what they are doing."

Democrats, in contrast, have delayed the release of any plan, arguing that other priorities like regulatory reform needed to be enacted first and fearful that any proposal could disrupt the still-fragile housing market. The only hint has come from Treasury Secretary Tim Geithner, who signaled that the administration still plans to include some kind of government role in the market.

"There is quite a strong economic case, quite a strong public policy case for preserving and designing some form of guarantee by the government to help facilitate a stable housing finance market," Geithner said in March. "But it can't be the one we have today. It can't be the one we lived with over the last decade. It's going to be significantly different."

Republicans may also have to change their tune if they do take power, some said. While Garrett and Hensarling are very conservative, it's unclear if all of their caucus would support the complete separation of the government from the mortgage market, especially if powerful grassroots political groups like the National Association of Realtors were to oppose such a move.

The GOP, too, would also have to be more careful not to upset the mortgage market when they do push their own legislation. That may make them more willing to compromise with Democrats, observers said. "It's in everybody's interest to reach a resolution in 2011," Chappelle said. "Democrats need to rebut the argument that they have let the GSE problem fester and if the Republicans do take control over the House and/or Senate, then they are going to assume some accountability so they are going to want to get a resolution, too."

Industry representatives said they expect both parties to tread carefully. "Any member of Congress regardless of their party, or ideology, is going to want to make sure homebuyers and homeowners can get mortgage financing; that goes to the heart of the matter," said Steve Verdier, a senior vice president for the Independent Community Bankers of America. "They are going to be very careful in what they do with Fannie and Freddie."

Bob Davis, an executive vice president at the American Bankers Association, agreed, but said he still thought the two sides would be far apart. "Both Democrats and Republicans face the same market and economic dilemmas but different views of policy can lead one into different solutions to deal with the same conundrum," said Bob Davis, an executive at the American Bankers Association. "The conundrums they face are the same. It will be equal for both parties, but there will be different policies on how to do that in housing policy."

The Obama administration, too, may surprise observers by taking a different approach than expected. Traditionally, the Democrats were seen as staunch defenders of Fannie and Freddie, but most top leaders, including House Financial Services Committee Chairman Barney Frank, now agree that they should be eliminated and replaced with some other structure.

"Democrats today have a different attitude toward the GSEs having seen what happened than was the case some years back," Davis said. "I don't think there are defenders anywhere for the system that existed previously."

Edward Pinto, a consultant and former chief credit officer at Fannie, agreed. "The political and policy environments are very different today than a year or two ago," said Pinto, who is now a fellow at AEI. "If Barney Frank can move a large distance on some of these issues, I would say, shouldn't housing interest groups re-examine their earlier positions based on the facts as we now know them? For example, is an explicit government guarantee of private mortgages a good idea? Both former Fed chairman and Obama administration adviser Paul Volcker and Federal Housing Finance Agency Acting Director Edward DeMarco recently warned against an explicit guarantee."