Be careful. A similar thing happened to us. We had to relocate and tried to sell just before the market tanked. We were never under water, but unfortunately the timing of our sale was unfortunate: We were just a tad too late to the party (i.e., the bottom had started to fall out of the market), so our realtor recommended renting it out until the market stabilized. This was in 2007. Although the rent didn't cover all of the expenses, we thought it sounded like something we could swing for a few months until we sold the house (NOT a smart choice on our part), and didn't want to be like "those people" who walked away from their responsibilities... but the property kept losing value, eventually went under water, and after 5 years as reluctant landlords (the market never did recover), we sold it at a short sale. (ouch)
The laws are changing all the time, so the exemption that Another Reader mentioned may or may not be in effect next year, but know that, under current law, if you rent out the place for too long and eventually do decide to sell it at a loss, you will likely have to pay taxes on the amount of debt that is "forgiven" in the transaction, because the place will no longer qualify as your "primary residence" (I believe under current law, you won't be liable for the taxes on the forgiven debt if you short-sell your primary residence).
I wish that we had just brought the $40k or so to the table back then. It would have spared us the trip down Landlord Lane and the pleasure of doing a short sale -- and the resulting hit to our credit.
Are you trying to "buy time" by renting it out now, at a loss? Would you ever consider living there again, or are you completely done with the place? By renting it out now (at a loss!), you might be only postponing the inevitable, and in our case, the inevitable was waaaay more costly, in every way than what would have occurred had we gotten rid of the place, one way or another, at the outset...