If you’ve been around long enough you may have noticed that mortgage rates — at or below 5% — are at their lowest level since the middle of the last century. It’s a result of the Federal Reserve’s program to purchase $1.25 trillion of mortgage-backed securities. But that program that is set to expire March 31 along with the home buyers’ credit — $8,000 for new home buyers and $6,500 for those who relocate — which is to expire April 30.

Already rates have risen in the last two weeks of December from 4.92% to 5.18% according to the Mortgage Bankers Association while applications for mortgages fell in the same period. Applications were 25% below their level at year end 2008.

If the Fed’s program ends March 31 it could push mortgage rates up a half to a full point and reduce the pool of buyers as ownership becomes more expensive. If the home buyers’ credit expires a month later, values could face a double whammy in the second quarter but also a fleeting stimulus in the first quarter as buyers rush to beat one or both deadlines.

Appraisal districts in 2010 will use sales from 2009 plus the first quarter of 2010 to support their Market Values published in May. With sales values in the last quarter of 2009 and the first quarter of 2010 artificially stimulated by the two threatened expirations, home owners who protest should be prepared to contest those sale valuations as ephemeral rather than permanent.