Fairfax County resident John J. O'Grady pleaded guilty yesterday to extorting $50,000 from a Northern Virginia banker for the safe release of the executive's daughter, whom he is accused of kidnaping in the bank's parking lot.

In exchange for his guilty plea, federal prosecutors dropped three less serious charges against him.

O'Grady, 33, told U.S. District Court Judge Albert V. Bryan Jr. in a soft, barely audible voice that he knows in prison and a $10,000 fine when he is sentenced next Jan. 2. O'Grady, who has described himself as unemployed and heavily in debt, also faces kidnapping, rape and related charges in Alexandria and Arlington.

Assistant U.S. Attorney Nash W. Schott told Bryan yesterday that O'Grady abducted 19-year-old Carol Lynn Drewer outside the First American Bank headquarters in McLean, where she worked, early in the morning of Sept. 23. O'Grady, the lawyer said, then demanded $50,000 ransom from her father, Milton Lee Drewer, who is president of the bank, in exchange for her release.

O'Grady told Drewer that he was a member of an unnamed "freedom group," and warned Drewer against informing police of the kidnapping if he wanted to see his daughter alive, Schott said.

The banker prepared a package of $50,000, mainly in $50 and $100 bills, and dropped the money in a garbage can at another McLean bank, following O'Grady's directions, the prosecutor said. Carol Drewer was released in the western section of Alexandria later that night, Schott said.

Four days later, O'Grady was arrested in a $90-a-day hotel suite in San Francisco and most of the money was recovered, Schott said. O'Grady also faces local charges in connection with the incident.

Alexandria officials have charged him with the kidnapping, rape and sodomy of a 26-year-old nursing student in an incident that federal officials have said was an unsuccessful kidnap attempt aimed against Drewer a week before the kidnapping.

O'Grady has pleaded innocent to the charges and his trail is scheduled for Jan. 26.