John O'Grady pleaded guilty in Arlington Circuit Court yesterday to committing nine felonies during last year's kidnapping of the daughter of a Northern Virginia banker.

O'Grady, 33, a former Fairfax County resident, is already serving a 15-year federal prison term for extorting $50,000 from Milton S. Drewer Jur., chairman of the First American Bank of Virginia and the father of Carol Drewer, the kidnap victim.

Last week, in an Alexandria state court, O'Grady was convicted of four other felonies, including abducting, raping and sodomizing a 27-year-old Alexandria nursing student in a related case. Sentencing on those charges is set for July 30.

Arlington Circuit Court Judge William L. Winston convicted O'Grady yesterday of four counts of robbery, four counts of using a firearm in the commission of a felony and one count of abduction with intent to extort money. Under Virginia law, the firearm convictions alone carry a combined minimum sentence of 10 years that cannot be reduced or served concurrently with any other sentence. Sentencing is scheduled for Aug. 14.

"He could get all the way from 50 years to five life sentences," said Arlington Commonwealth's Attorney Henry Hudson, who prosecuted the case.

Carol Drewer was abducted Sept. 23 from a parking lot at the First American Bank's Tysons Corner headquarters, where she and her father worked. She was released 14 hours later after her father had paid a $50,000 ransom and she had been forced to cash four checks totaling $1,200 at branches of the bank.

O'Grady was arrested four days later in a $90-a-day San Francisco hotel room atop Nob Hill where FBI agents found a .22-caliber revolver that had been purchased at a Virginia gun shop and recovered $33,000 from a safe-deposit box. FBI Agent Tom Fitzpatrick testified yesterday that more than 150 bills taken from the box had the same serial numbers as those given in the ransom.