WASHINGTON — Even preschoolers are getting suspended from U.S. public schools — and they’re disproportionately black, a trend that increases up through the later grades.

Data to be released today by the Education Department’s civil rights arm finds that black children represent about 18 percent of children enrolled in preschool programs in schools, but they represent almost half of the students suspended more than once.

Six percent of the nation’s districts with preschools reported suspending at least one preschool child.

Advocates have long said that get-tough suspension and arrest policies in schools have contributed to a “school-to-prison” pipeline that snags minority students, but much of the emphasis has been on middle school and high school policies.

This data shows the disparities starting in the youngest of children.

Earlier this year, the Obama administration issued guidance encouraging schools to abandon what it described as overly zealous discipline policies that send students to court instead of the principal’s office.

But, even before the announcement, school districts have been adjusting policies that disproportionately affect minority students.

Overall, the data shows that black students of all ages are suspended and expelled at a rate that’s three times higher than that of white children.

Even as boys receive more than two-thirds of suspensions, black girls are suspended at higher rates than girls of any other race or most boys.

The data doesn’t explain why the disparities exist or why the students were suspended.

Education Secretary Arne Duncan and Attorney General Eric Holder were to appear at J.O. Wilson Elementary School Friday in Washington to discuss the data.

“It is clear that the United States has a great distance to go to meet our goal of providing opportunities for every student to succeed,” Duncan said in a statement.

Nationally, 1 million children were served in public preschools, with about 60 percent of districts offering preschool during the 2011-12 school year, according to the data.

The data shows nearly 5,000 preschoolers suspended once. At least 2,500 were suspended more than once.