Teacher performance evaluations at a Fairfax County high school were falsified and the principal has been held responsible after an internal investigation, district officials said yesterday.

Discovery of the doctored evaluations prompted a districtwide probe into the integrity of the county's touted merit pay program. But officials said they concluded the problem was limited to the evaluations of three teachers in the single school.

The incident is the first abuse of Superintendent Robert R. Spillane's merit pay program to become public since it began in 1986. The landmark pay-for-performance system has been praised across the nation as an important educational improvement, although teachers and others have complained that it is open to corruption and favoritism.

Assistant Superintendent Dolores Bohen, the school district's chief spokeswoman, said the 1988 evaluation reports for the three teachers at JEB Stuart High School were changed to lower their performance ratings. Bohen would not say who district officials believe altered the evaluations. But she said "appropriate action" was taken against the person who was principal of the school at that time because he was in charge.

"The principal is the central person in the evaluations," she said. "The principal is responsible for whatever happens with the evaluations that occur under him."

Although she would not identify him by name, John C. Randall Jr. was the principal in the 1987-88 school year, when the evaluations in question were filed. Randall retired from Fairfax schools in 1989, a year before the altered documents were discovered, and has since become an associate school superintendent in Prince William County.

Randall twice declined to be interviewed yesterday, first on the telephone and later when a reporter went to his home. "Read my lips," he said the second time. "I'm no longer employed by the {Fairfax} school system."

Sources said an official letter about the incident was placed in Randall's Fairfax personnel file, but because he no longer works in Fairfax, no further action could be taken.

The investigation was sparked by the discovery in June 1990 of forms filed in the district's personnel office in 1988 that incorrectly listed three Stuart teachers as having received the second-highest performance ranking, "skillful," instead of the top grade of "exemplary." Another copy of the evaluations kept at the school correctly indicated that the teachers had been rated "exemplary," as they had been told.

When an evaluation is completed, the teacher and the principal sign the report. But when shown the personnel office copies of the evaluations, the teachers said the signatures were not theirs, sources said.

Several administrators had access to the forms. Randall signed all evaluations, and his signature was on both the authentic and the altered evaluation forms of the three teachers, sources said.

At the time, both rankings were high enough to bring the teachers 9 percent salary bonuses -- about $4,500 a year for the average teacher -- and all three received the extra money.

For unrelated reasons, the system has since been revised so that someone whose ranking is changed would notice it because the paycheck amount would change.

Under Fairfax's performance evaluation system, teachers applying for the merit bonus are observed in their classrooms by administrators or other teachers six times and judged in eight areas, such as knowledge of subject matter and controlling student behavior.

The school principal rates the teacher based on those observations. In the case of the three JEB Stuart teachers, the ratings they were officially given were improperly changed later.

Bohen said officials conducted an exhaustive check of the records of 4,000 of the county's 8,700 teachers and found no other improper changes.

The investigation began when one of the three Stuart teachers, now working in a school district office, checked a computer printout to see when she would be reevaluated and noticed her rating had been changed.

Although that investigation began in late spring, the School Board was not notified until it was complete earlier this month, irking some members who said they should have been told sooner.

"I was upset it was so long before the board was told there was a problem," said Vice Chairman Laura I. McDowall (Annandale).

The three teachers were judged during the first districtwide evaluations under the new merit pay program. The names of the teachers could not be learned, and they declined to comment through an intermediary.

Although school-by-school breakdowns have never been released, nearly every teacher who applied for merit pay at Stuart was rated high enough to receive it that year, according to some who worked at the school.

Although Spillane has said that no quota system would be used to limit the number of teachers receiving high rankings, he also told principals that not every teacher should receive the highest rating. Some county supervisors, among others, feared that so many teachers would receive high ratings that the bonuses would put a strain on the school district's budget.

Spillane could not be reached for comment yesterday.

Randall, 50, retired in summer 1989 after 25 years with Fairfax schools, saying he wanted to relax.

Shortly thereafter, he took a job as a high school principal in Montgomery County and explained to a reporter that he could collect both retirement benefits and a salary in that way. He took his current job in Prince William on July 1. Prince William Superintendent Edward L. Kelly could not be reached for comment.

Critics of the merit pay program said the incident proves that the system is ripe for abuse and demonstrates that principals feel pressure not to give too many teachers high ratings.

"The only {reason} that comes to my mind is that {an administrator} was told there were only so many exemplary ratings he could award and he had given out too many," said Rick Willis, executive director of the 6,900-member Fairfax Education Association, the teachers union.

"It was just a matter of time before something like this happened. I don't trust their internal investigation, and I don't trust them," he said.

School officials dispute that.

"It's really an isolated incident," said School Board Chairman Kohann H. Whitney (Centreville). "I don't think there's a problem with the whole system. We're a very large bureaucracy, and in large bureaucracies things are not always absolutely perfect."

Bohen said the resolution of the problem shows that the system works. "It really doesn't speak to performance evaluation or merit pay," she said. "It speaks to human nature. Anything that depends on people is going to be subject to abuse . . . . The important thing in this case is that the system of checks and balances is in place and works."