Senators hammered out a compromise that aims to stabilize the U.S. housing market and help hundreds of thousands of homeowners avoid foreclosure. But critics warn the plan puts taxpayers at greater risk than disclosed. They say if home prices keep falling for years, the government would lose billions of dollars. The plan directs the two largest buyers of mortgages, Fannie Mae and Freddie Mac, to give the government hundreds of millions of dollars each year, and to insure risky loans. Both have suffered huge mortgage losses.