nd if the limit on loans backed by a government-backed housing finance entity like Fannie Mae is raised from $417,000 to the full $729,750 she has been hearing about, Ms. Kilgore said, “we will be able to get a 30-year fixed mortgage for less than what we’re paying now plus our homeowner’s dues.”The temporary change in the loan limits is not about to revive the housing market on its own. But in some of the higher-priced regions of the country that have been hit hardest by the flagging real estate market, it could make a big difference. For if anything is going to breathe new life into the local housing economy in places like the San Francisco Bay Area, San Diego, Washington and Boston, it is home buyers emboldened by the prospect of larger loans at lower interest rates.