* Dollar falls as credit worries persist

* Investors focus on Fannie and Freddie

* Bernanke, Paulson comments mildly dollar-positive (Updates prices, adds comments, byline)

By Gertrude Chavez-Dreyfuss

NEW YORK, July 10 (Reuters) - The U.S. dollar fell against a basket of currencies on Thursday, weighed down by renewed credit worries after shares in major mortgage finance sources Fannie Mae and Freddie Mac tumbled on capital concerns.

Stress in financial markets intensified after Fannie Mae (FNM.N: Quote, Profile, Research) and Freddie Mac (FRE.N: Quote, Profile, Research) stocks plunged to their lowest since 1991. The yield spread premium for the larger Fannie Mae rose to its highest since before the Federal Reserve's bail-out of U.S. investment bank Bear Stearns Cos in March.

"This is all Fannie and Freddie, renewed credit concerns overall, and general risk aversion that we have been seeing for the week," said Ron Simpson, director of currency strategy at Action Economics in Tampa, Florida.

"We saw dollar/yen sold down to below 107. Everybody is still nervous," he added.

In late morning trading, the dollar index, tracking the greenback's performance against six major currencies, fell 0.1 percent to 72.511 .DXY.