With one-quarter of the school year over, city school officials are taking the unusual step of transferring 50 teachers to different schools Monday.

The moves, which will affect many more than 50 classrooms in the city, are meant to address crowding in some classrooms and under-enrollment in others.

About 122 teachers were mailed letters last week, telling them to report to a different school Monday. But by yesterday, the number of teachers that would be moved had been significantly reduced, said Sheila Dudley, head of human resources for city schools.

"We have made quite a few adjustments. ... Every hour the numbers change," she said. "This is a dynamic process." The teachers being transferred are primarily new teachers who have just gotten adjusted to their students and schools.

"They were very difficult decisions that had to be made, but fiscally we can't continue to have an overage of teachers in some schools and vacancies at other schools," Dudley said.

While the number of teachers being switched to a new classroom is small -- 50 of 7,000 across the system -- the effects will ripple across many classrooms.

Teachers were selected to be transferred based on seniority. As a result, an elementary school that has too many fourth-grade teachers might have to transfer a second-grade teacher because that teacher is the most recently hired. Then, a fourth-grade teacher would have to be moved to second grade. In this way, two classes would be affected in the building losing one teacher as well as the class in the school receiving the new teacher.

Several principals who have lost or gained one teacher said the effect would not be that deleterious.

Patterson High School in East Baltimore is losing one science teacher.

"I am OK with it because my enrollment is down. It is not really going to be a hardship," said Patterson High School Principal Laura Deanna.

At Winston Middle School, Principal Eldon Thomas said her school would be gaining a teacher. "I had a vacancy and as a result of this, it is being filled. I am not losing anybody," she said.

Thomas said she had a substitute staffing the vacant position.

Such midyear moves have not been standard practice. In previous years, when a school ended up with fewer students and more teachers than its allotment based on enrollment, the system allowed the teacher to stay for the rest of the year. But this year, the system has decided to strictly enforce the limits in elementary and middle schools.

"With our current fiscal condition, we no longer have that luxury," Dudley said. In the high schools, there is a glut of teachers -- about 35 -- who will remain where they are unless a teacher leaves or resigns from another high school. Teachers in elementary grades are not usually certified to teach in high school or vice versa.

Even after the moves, the city will have to hire elementary school teachers. A job fair is being planned for this month, Dudley said.