Karen Ann Robb, who was rescued by police during a suicide attempt but then was charged with possessing half a gram of cocaine found in her purse during the rescue, pleaded guilty yesterday to a reduced charge and was fined $100 by an Arlington judge.

The outcome was satisfactory to Robb, the 25-year-old office employe of a Capitol Hill real estate office, who said she had not wanted a felony conviction "hanging over my head . . . With this misdemeanor I can be up front with any potential employer."

Robb could have been sentenced to up to 10 years in prison for cocaine possession. The misdemeanor to which she pleaded guilty is possession of tetracycline - a commonly prescribed antibiotic - without a prescription.

Robb, who said she no longer has thoughts of suicide, has said that when she attempted to kill herself May 3 she was despondent over family problems and the fact that she had to drop out of the University of Maryland because of low grades. She said she intended to jump off Key Bridge but prevented from going there because police had placed a disabling "boot" on her car.

Robb said she then went to her boyfriend's house in Arlington, turned on the gas oven and put her head inside. A house painter working at the house discovered her and called police and a rescue squad. When a police officer emptied Robb's purse to determine her identity and whether she had taken any medication, he discovered the cocaine inside a film canister. Robb maintained she was given the cocaine by a friend "to help me stay up all night because I was going through some problems."

Prosecutors had offered to allow Robb to plead guilty to the felony cocaine charge under a first offender program that would erase her arrest record after a year if she had no further drug charges.

But Robb said she preferred to have nothing "hanging over my head."

Assistant Commonwealth's Attorney Karen A. Henenberg said, "I think there are mitigating circumstances due to the suicide (attempt) and she does have problems and she is a first offender. But (the first offender program) was unacceptable to her . . . We felt that there was no other alternative but to prosecute."

Robb described herself as "one of those people who smokes marijuana once a year, and I've never purchased a drug in my life."

Last month Arlington Circuit Court Judge William L. Winston said the officer who found Robb with her head in the oven "would have been remiss in his duties" if he had not searched the film container in Robb's purse while determining her identity and whether she had taken any drugs."