Auditors investigating Fairfax City's tangled finances have concluded that nearly $160,000 is missing from accounts once supervised by former treasurer Frances L. Cox, whose embezzlement trial is scheduled to start on Monday.

Cox, who left office Dec. 31, was indicted in June. The felony indictment by a Fairfax County grand jury gave no specific dollar amount, but city officials said at the time they believed about $150,000 was unaccounted for.

The auditing firm, Murray Jonson and White Ltd. of Arlington, said in a report to City Manager Ed Wyatt that it was unable to locate $157,751 in revenues. The report also was sharply critical of office procedures in effect during Cox's 27-year tenure.

"Internal controls which serve to safeguard the assets of the city appeared to be weak, with few of the fundamental controls in place and operational," the firm said.

"The weak controls, missing or distorted records, other uncertainties, and audit work on taxes receivable combine to indicate that the balance due to the city of Fairfax is not an accurate amount."

Cox's successor, Ray Birch, quit the post after three weeks, complaining he had found cash stuffed in drawers, checks left unrecorded and a $156,000 overdraft in the city's bank account.

Mayor John Russell yesterday declined comment, citing Cox's upcoming trial in Fairfax Circuit Court. Cox's lawyer, Northern Virginia Del. John H. Rust Jr., was unavailable, an office employe said. Cox pleaded innocent to the charge at her arraignment in June.

The recently completed audit, which a company employe said yesterday was begun about a week before Cox left office, was carried out without Cox's cooperation, the firm said.

There are five announced candidates running for the $30,000-a-year treasurer's job in this November's election. The City Council appointed John W. Coughlan to fill the position in the interim.