The Prince William County public schools auditor will increase the number of surprise inspections conducted each year.

School Board Chairman Milton C. Johns (At Large) and members Lisa E. Bell (Neabsco, Betty D. Covington (Potomac) and Gilbert A. “Gil” Trenum Jr. (Brentsville) discussed minor changes to the audit program Wednesday. The program, launched in 2010, has been effective in refining spending practices while holding accountable those in charge of budgets, officials said.

The audit program gained attention recently when the school system’s lone auditor, Vivian McGettigan, helped uncover embezzlement at Kilby Elementary School. Last week, The Washington Post reported on misuse of credit cards at Potomac Middle School in Dumfries, where five administrators ran up charges, including large meal bills and an expensive hotel stay, according to an audit.

McGettigan said most audits show that Prince William administrators are managing their budgets effectively. Five elementary school audits presented Wednesday unveiled few issues with accounting procedures and money management, McGettigan said.

But she told board members that the most effective way to deter fraud was with unannounced audits. She will increase audits from 10 to 15 schools per year, she wrote in a proposal, which was adopted.

That plan means McGettigan will take a closer look at the 700 or so credit cards the school system has. Credit cards are “high risk due to the after-the-fact review of purchases and the reliance on individual card holders to ensure that items purchased are appropriate,” according to the proposal.

McGettigan said more audits would require more staff members. The school system’s 93 schools could be audited every three years, instead of six. A three-year rotation “would be ideal,” McGettigan wrote.

Superintendent Steven L. Walts said it’s unlikely the school system would be able to increase the auditor’s staff next year. Last year, a divided School Board wrestled with giving teachers raises. Also, the state mandates that Prince William hire more teachers to keep up with growth.

The county has the largest class sizes in the state, and hiring more teachers while retaining experienced ones is a persistent issue in a tough budget climate.

Walts said that although he and the School Board haven’t decided about staffing for next year, additional resources would probably be focused on the classroom.

“In a time when budgets are very close . . . we want the majority of our resources to go to students,” Walts said.