An experimental program to select outstanding teachers for merit raises should be redesigned before it is expanded, the Fairfax County School Board was told in a staff evaluation last night.

The experiment, just completed at a cost of $300,000, was planned so poorly that "some confusion, inconsistency, miscommunication and frustration" resulted, but it offers the potential to improve teaching and supervision, the staff report said.

The staff recommended the program be halted while a task force rewrites it by early next year.

School Board members who commented indicated they probably will agree with the staff's assessment when the board votes next month.

"I hope we can hang onto the good positive aspects that have come out," said board member Joy G. Korologos. Member Anthony Cardinale agreed.

Teachers and administrators complained that performance reviews took so much time that their other duties suffered, James Shinn, director of the system's office of employment services, told the board. Some teachers said the rating system weakened morale, he said. Others questioned whether the system of rating teachers on a scale of 1 to 5 could accurately measure performance.

But other teachers reported that they learned useful lessons from the observation teams, Shinn said.

The experiment involved 62 teachers at five county schools, who agreed to be reviewed by three-member teams in return for a $300 stipend. No salary increases were budgeted. Donna Caudill, president of the Fairfax Education Association, told the board an informal survey of her teacher group's members found only one who would be willing to sign up for evaluation next year.

In Arlington County, the School Board decided this week not to go ahead with merit pay, but to offer teachers other kinds of incentives.

Nationally, President Reagan and some other political leaders, including Virginia Gov. Charles S. Robb, are pushing for merit pay as a tactic to retain good teachers and improve the schools' battered public image.

Polls show the public favors the concept. But teacher unions generally oppose merit pay, contending it is impossible to fashion objective standards by which to judge teachers.

In other business, the School Board named Doris Torrice, one of four area superintendents, to be one of two deputy superintendents of the region's largest school system.

Torrice will become deputy superintendent for support services on Monday. For four years, she has been superintendent in Area One, which includes schools in the eastern part of the county.

Torrice joins the top rank of the school administration at a time when the superintendent, the other deputy superintendent, three of the 10 School Board members and its nonvoting student representative also will be new to their jobs.

Jay Jacobs, now assistant superintendent for career and resource development services, was named last night to succeed Torrice as Area One superintendent.