A jury last night convicted former Fairfax City treasurer Frances L. Cox of embezzling city funds and recommended that she be imprisoned for 10 years.

Deputy sheriffs led a grim-faced Cox, 56, away to jail immediately after the verdict when Circut Court Judge Barbara Keenan revoked Cox's bond. "The sentence of the jury is extremely severe," said Keenan, who set Cox's sentencing for Oct. 15.

Cox's attorney, John H. Rust Jr., said he would have no comment on whether the verdict would be appealed pending the formal sentencing at which the judge could accept the 12-member jury's recommendation or impose a reduced sentence.

"Justice was done," said Deputy Commonwealth's Attorney Steven Merril, when the jury announced its verdict after three hours of deliberation. "It was a fair sentence." He said that if the judge imposes the 10-year sentence Cox could be eligible for parole after serving 20 months. Cox could have received up to 20 years in prison.

During the four-day trial, Rust had portrayed Cox as a dedicated public servant who may have been incompetent and kept sloppy accounting records but was not dishonest. Merril had argued that Cox, who had been charged with embezzling an unspecified amount of money over a 30-month period, was a dishonest politician who stole from the public to support a high life style.

In his closing arguments yesterday, Merril told the jury that Cox deposited about $200,000 in cash in her personal bank accounts in 1980-81 -- twice the amount he earlier had alleged she stole and 10 times the minimum amount of money he said was missing from city accounts in 1981.

"She lived a good life," said Merril. "She lived high -- that's why she did it." He ticked off a list of checks Cox wrote from her personal bank accounts that he said demonstrated her life style: $4,000 to Elizabeth Arden Beauty Salon, $3,000 to Elizabeth Arden, $600 to Neiman-Marcus, $500 to Neiman-Marcus.

"There can't be any doubt we have a dishonest public official who has stolen money from the City of Fairfax," Merril said. . . . There's nothing worse than a dishonest politician. It eats at the very core of our government."

Prosecutors argued that Cox substituted cash received in the treasurer's general fund with checks from real estate and personal tax funds in an attempt to cover the missing money.

Rust yesterday described Cox as a poor bookkeeper whose office was chaotic and disorganized. "Maybe she wasn't up to being treasurer anymore," Rust said in his closing arguments. "When you cut corners, it's not good accounting. But it's not a crime."

"Mrs. Cox is a politician, she's not an accountant," said Rust of the woman who was city treasurer 27 years before she was defeated for reelection last fall. "She started out in a small town and . . . the town grew up around her. Maybe she didn't adjust to the sophisticated, cosmopolitan techniques of accounting now required for the city."

Rust argued that prosecutors had only investigated the city's general fund accounts and did not look into other funds where the allegedly missing money may actually have been credited. He said the prosecution never proved the city actually lost the money.

Merril countered that even the most conservative interpretation of evidence showed that the city was missing at least $20,000. Rust leaped on the large difference between the $20,000 figure and large cash deposits in Cox's personal bank accounts, where the prosecution alleged Cox deposited stolen funds.

"We don't know what the top amount is -- Lord knows what that is," said Merril, as a standing-room-only crowd filled the courtroom. "The $20,000 was the minimum amount that was taken in this scheme."