Assembled in special session on a hot afternoon in late June, the school board of this Los Angeles suburb spent five seconds inaugurating one of the decade's most controversial educational changes.

The board approved Pasadena's first master teachers, 10 women and three men, to join the nation's first extensive test of incentive pay for teachers. But that selection process has turned the program here in a direction not anticipated by those who proposed it: Teachers are being selected not on the basis of how well their students learn but on how tactfully and enthusiastically they deal with colleagues.

The experiment began after months of difficult negotiations between teachers and administrators and a crash selection process to avoid losing state funds. It started with almost no public notice, despite the national controversy surrounding it and President Reagan's endorsement of merit pay as the first step in reviving high standards in U.S. public education.

Each "mentor" teacher under California's new law would be paid $4,000 extra in the 1984-85 school year. The 13 Pasadena teachers, for their demonstrated excellence, would receive $2,000 for the semester that ended just as they were chosen, for a total bonus of $6,000.

But only 43 of the city's 900 teachers applied to be mentor teachers, in part because of the last-minute rush to pick the first group before summer vacation. The selection committee had time for only brief visits to the classrooms of teachers already chosen.

"The timing was terrible, horrible," said Maggie Gardner, a bilingual resources teacher who headed the selection committee.

During the debate over the state law, the Pasadena negotiations and the three-week selection process, however, teaching ability became just one of several considerations.

"There are teachers out there who are absolutely glorious teachers, but act like princes in their own little castles," said Joe McFadden, an English teacher who represented high school faculty on the selection committee.

Such people did not survive the selection committee interviews.

Many Pasadena teachers accepted the idea of a mentor program with all the enthusiasm of an errant pupil kept after school. They acknowledged that it might do some good but were uncomfortable with it. Representatives of the United Teachers of Pasadena insisted on a teacher majority on the selection committee, as provided by state law. The extra money, the law said, would be paid not strictly for merit but for mentor help in developing lesson plans and training new or struggling teachers.

The new mentor teachers have received their first bonus payment. Some have begun work on a new teachers' manual. Requests have come in from teachers for mentor assistance.

Teachers unions in other states had blocked merit-pay plans, arguing that the selection process would bog down in favoritism and faculty politics.

Antoinette Dunbar, an elementary school principal who was one of three administrators on the Pasadena committee, said its four teachers "were eager to remind us that they had the majority rule there."

For her part, she said, "it was hard to stop playing administrator."

But committee members found that their disagreements rarely split along teacher-administrator lines.

The application for mentor teacher sought information on college degrees, teaching experience and other professional activities. It asked about the applicant's experience in helping other teachers and the applicant's personal strengths and plans for the program.

It asked applicants to measure themselves against the state's definition of a mentor teacher: "exemplary teaching ability including effective communication skills, subject-matter knowledge and mastery of a range of teaching strategies necessary to meet the needs of pupils in different contexts."

Twenty-five applicants were called in for half-hour interviews.

When hiring teachers, "I always thought Pasadena had the worst interview committees I had ever seen," said Bill Hyland, a sixth-grade teacher on the committee. "One question they used to ask was, 'What do you think of discipline?' That's like asking, 'What's the weather?' "

He insisted that the committee probe each applicant's attitude toward dealing with struggling teachers and ask for solutions to hypothetical problems.

"I was grilled," said Kim Pollard, a successful applicant who had been teaching for 27 years. "They worked us over."

High-school history teacher Donald Van Orman, another mentor, said, "The questions they asked got right to the point."

In the end, committee members found themselves in surprising agreement, even on their unexpected decision to name 13 mentors instead of the 19 the budget allowed. Chairman Gardner said she and another member abstained in two cases rather than contradict the majority that did not share their high opinion of an applicant.

"There were no close votes," she said.

The winners were picked from throughout the system, although Dunbar felt that the lower grades were underrepresented because "elementary teachers tend to undersell themselves."

The chosen mentors comprised three teachers from elementary schools, two from junior highs, seven from high schools and one from a special-education school.

The numbers of applicants remained far below what committee members had hoped, particularly as the law allowed for as many as 45 mentor teachers in a school district of Pasadena's size.

"Some very fine teachers did not apply," McFadden said, "and some who were not the world's greatest teachers did apply."

Selection committee member Alma Hill, who teaches second grade, was not certain if she would ever apply, citing the particular kind of merit that this program had fixed upon.

"I like the classroom; I like teaching children," she said. "I don't particularly care for working with adults."