JACKSON (AP) — A judge on Tuesday ordered a small south Mississippi school district to stop allowing hundreds of white students to transfer out of majority black schools, calling the practice a violation of a desegregation order and federal law.

U.S. District Judge Tom S. Lee sided with the Justice Department in its complaint against the Walthall County School District.

The district’s schools in Tylertown are about 75 percent black with 730 students. The Salem Attendance Center is 65 percent white with about 650 students in grades K-12. Salem and the Tylertown schools are about 10 miles apart.

The Justice Department contended the school district had, for years, allowed hundreds of white students to transfer from Tylertown to Salem.

Thomas E. Perez, assistant U.S. attorney general for civil rights, said Tuesday that the actions by the school district led local residents to regard certain schools as ‘‘white schools’’ or ‘‘black schools.’’

He said officials in certain district schools grouped white students together in particular classrooms, resulting in large numbers of all-black classes at every grade level.

in those schools.

Walthall County School District Superintendent Danny McCallum was not immediately available for comment. A secretary in his office said McCallum had not seen a copy of the judge’s order.

McCallum has said that because of the way the school district lines are drawn, some students who are assigned to Tylertown actually live closer to Salem. He has said that was the reason for the transfers.

Clennell Brown, president of the Walthall County NAACP, also could not immediately be reached for comment. Brown has said he informed the Justice Department each time a transfer was approved.

Perez said Lee’s order requires the school district to change its transfer policy to only allow transfers to a school outside a student’s residential zone only if students can justify it as a well-documented medical emergency or if students have a parent working full-time at a school outside their zone.

Exceptions also would be made for students transferring to a school where they would be a racial minority. For example, a white student attending a majority white school would be allowed to transfer to a school where the majority of students are black.

Lee also ordered the district to adopt policies that would ensure students are not assigned to segregated classrooms and have the policies in place for the 2010 fall term. He said the new policy would not apply to students who have already transferred to Salem Attendance Center and will graduate in 2011.