WASHINGTON — Michelle A. Rhee, the Washington schools chancellor whose confrontations with the teachers’ union made her a polarizing symbol in school reform battles nationwide, is stepping down, a city official said.

Her position had been in doubt since last month’s Democratic primary, in which her approach was an issue that divided the city largely on racial lines. Mayor Adrian Fenty’s strong support of the chancellor was a factor in his loss to Vincent C. Gray, the chairman of the City Council.

Ms. Rhee and Mr. Gray will announce her resignation together on Wednesday, according to the city official, speaking on the condition of anonymity. The official said the joint announcement was a compromise resulting from a standoff in which Ms. Rhee refused