Sandy-hit Nassau and Suffolk property owners must apply for a special two-year tax credit or refund by the Jan. 21 deadline, county officials said Saturday.

"Nassau County will adjust, retroactively, any property tax assessment to account for losses in value due to Superstorm Sandy," Nassau County Executive Edward Mangano said in a statement.

advertisement | advertise on newsday

Suffolk County Executive Steve Bellone spokeswoman Vanessa Baird-Streeter said residents were encouraged to apply with their town tax assessors.

Local governments could opt into this tax relief program for home and commercial property owners for the 2012-13 and 2013-14 tax years under a measure Gov. Andrew M. Cuomo signed in October.

The U.S. Department of Housing and Urban Development is footing the bill through Community Development Block Grants, Nassau Chief Deputy County Executive Rob Walker said by email.

So far, 6,200 Nassau property owners have applied for $21 million of tax relief. Savings can reach several thousand dollars, depending on damage, he said.