AS we all move forward with our New Year's resolutions, it's a good time to remember the promises our politicians have been making about the American mortgage market. The Obama administration, at a conference last August on the future of housing finance, pledged to have, come January, a plan for Fannie Mae and Freddie Mac, the mortgage giants that are now wards of the government. Congressional Republicans, in their recent position paper, made an even bolder resolution: to build a mortgage market that ''does not rely on government guarantees'' and ''does not make private investors and creditors wealthy while saddling taxpayers with losses.'' This latter promise is pleasing populist rhetoric. The problem is, it may be neither politically nor practically feasible. Even if we forget about the gigantic near-term problem -- namely, that the federal government is in the housing market mainly because most banks simply won't issue mortgages that can't be guaranteed by Fannie, Freddie or the Federal Housing Administration -- there's the fact that federal involvement in housing has been a constant since the 1930s. A market without government support would almost certainly involve the demise (for most of middle-class America) of that populist favorite, the low-cost 30-year fixed-rate mortgage. [ABSTRACT FROM AUTHOR]