NEW YORK, July 9 -- Metromedia Fiber Network Inc. said Citigroup Inc. had granted it a conditional one-month extension of a commitment letter for a $350 million credit facility. The letter of extension to July 31 from June 30 gives Metromedia additional time to line up commitments from other lenders in the amount of $287.5 million.
   The company said it is negotiating with other lenders to raise the additional funds for the total $350 million credit facility.