U.S. single-family home prices fell for a fifth straight month in November and could plumb new lows soon, a closely watched survey showed on Tuesday.

The Standard & Poor's/Case-Shiller composite index of 20 metropolitan areas declined 0.5 percent in November from October on a seasonally adjusted basis, though it was not as sharp as the 0.8 percent fall expected by economists.

Prices have fallen 1.6 percent in the past year, sharper than the 1.4 percent predicted by economists polled by Reuters.

Sixteen of the 20 cities showed annual price declines in November, while 19 of 20 cities showed monthly price drops.

The housing market has been struggling since home-buyer tax credits expired earlier this year. To take advantage of the tax credits, buyers had to sign purchase contracts by April 30.

A double-dip could be confirmed before Spring, said David Blitzer, chairman of the index committee at S&P. Blitzer defined a double-dip as both the 10 and 20-city composite indices setting new post-peak lows.

He noted that the 10-city index is 4.8 percent above its April 2009 low while the 20-city index is just 3.3 percent higher than its low that same month.

Unadjusted for seasonal impact, the 20-city index fell 1.0 percent in November after a 1.3 percent decline in October.

I find it hard to believe that if we get a double dip in home prices we could get the consumer back in a meaningful way. Right now it seems like a coin toss as to whether that's likely. So I'm disappointed, said Uri Landesman, president of Platinum Partners in New York.

(Reporting by Corbett B. Daly; Editing by Chizu Nomiyama &Theodore d'Afflisio)

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