Fairfax County prosecutors dropped two charges of fraudulent credit card use yesterday against Debra D. Hill, the Reston woman police arrested in October on charges of filing a false report that she had injured an eye using contaminated Visine A.C. eyedrops.

Assistant Fairfax Commonwealth's Attorney Raymond Brownelle told a General District Court judge that investigators were unable to locate the witnesses they needed in the three-year-old credit card fraud cases against Hill. He asked Judge Frank B. Perry to dismiss the charges and, after a brief hearing, the judge agreed.

Although Hill allegedly used a credit card fraudulently at two Fairfax City stores in 1979, police didn't serve the warrants in the case until Nov. 1 -- the same day Hill was charged with giving county police a false report of the eyedrops incident.

Hill, 30, has said she is innocent of the Visine charges on which she faces trial Dec. 17 in Fairfax Circuit Court. She is accused of a misdemeanor, giving police a false report that eyedrops she had purchased at a Herndon Drug Fair store were laced with chemicals that injured her eye.

At the same time Hill was charged in that case, police served her with two counts of credit card fraud for 1979 purchases of $491.39 at a shop called Lady Bug and $113.62 at Wild and Wooly Needlecrafts. Brownelle said yesterday Hill allegedly used another individual's credit card, but said investigators have been unable to find that individual to be a witness.

Hill also was charged earlier this month with passing a $521.29 bad check in Prince George's County. Five days later, she was charged with five counts of passing bad checks totaling $1,573.98 in Fredericksburg. Hill said she has yet to enter any pleas in those cases.