* Credit concerns fuel global equity sell-off

* More writedowns seen at Lehman Brothers

* Home Depot beats profit estimates

* PPI, housing starts on tap (Fixes wording in first paragraph)

By Ellis Mnyandu

NEW YORK, Aug 19 (Reuters) - U.S. stock index futures fell on Tuesday as fears that the U.S. housing slump will spawn more losses for the financial sector caused investors to pare back risk.

As a result, Wall Street was poised to extend declines seen in Asia and in Europe.

Adding to gloom about the financial sector was a forecast by JPMorgan Securities that Lehman Brothers LEH.N, a U.S. investment bank, will likely take a further $4 billion of write-downs in the third-quarter due to losses stemming from sour mortgage-related investments.

Additionally, worries about the stability of home finance providers Fannie Mae (FNM.N: Quote, Profile, Research) and Freddie Mac (FRE.N: Quote, Profile, Research) persisted.