Arne Duncan, the Chicago schools superintendent known for taking tough steps to improve schools while maintaining respectful relations with teachers and their unions, is President-elect Barack Obama’s choice as secretary of education, Democratic officials said Monday.

Mr. Duncan, a 44-year-old Harvard graduate, has raised achievement in the nation’s third-largest school district and often faced the ticklish challenge of shuttering failing schools and replacing ineffective teachers, usually with improved results.

He represents a compromise choice in the debate that has divided Democrats in recent months over the proper course for public-school policy after the Bush years.

In June, rival nationwide groups of educators circulated competing educational manifestos, with one group espousing a get-tough policy based on pushing teachers and administrators harder to raise achievement, and another arguing that schools alone could not close the racial achievement gap and urging new investments in school-based health clinics and other social programs to help poor students learn.