D.C. officials revised and clarified their figures Tuesday on school system employees whose jobs will disappear next month, saying that of 745 affected by changing staffing needs, 384 are unionized teachers, librarians, counselors or social workers who will have to apply for other jobs in the system.

The District announced Monday that about 660 teachers and support staff would have to reapply for other jobs in the system because of changes in school budgets, enrollment or programming. The annual process, known as “excessing,” is designed to bring staffing at schools in line with enrollment and funding.

But school officials caused some confusion in the original announcement by omitting some employees from the original count and failing to specify exactly how many teachers and other instructional staff were at risk.

Jason Kamras, chief of the school system’s office of human capital, stressed in an interview that the elimination of the jobs did not constitute layoffs and that the number of staff “excessed” is in line with those in past years. Many of the teachers, he said, have a good chance of finding other positions in the school system.

“Based on what we’ve seen, I expect a high percentage to be picked up at other schools,” Kamras said.

But this year’s excessing drew a harsh reaction from teachers and union leaders, who characterized it as a slow-motion firing. Under the terms of the new labor contract, excessing decisions are to be made based on performance, not traditional seniority guidelines. And where excessed teachers were once guaranteed other jobs in the system, new contract provisions also allow principals to pass them over in favor of newly recruited, and often younger, teachers.

“If you’re old and white, old and black, old and anything, you are at risk,” said Emily Washington, a veteran teacher and union activist.

Kamras said that such an idea was “absolutely false.”

Kamras said that those excessed were not necessarily poor performers but might have been good educators caught up in a program switch, such as a school’s decision to offer a different foreign language next year or to add extra early-childhood classrooms.

“You have a lot of strong people in this pool that principals are going to be excited about picking,” he said.

An estimated 600 additional teachers could face dismissal later this year for low scores on the IMPACT teacher evaluation. These are teachers who scored at “minimally effective” levels last year, and face termination if they make low scores for a second year in a row.