WASHINGTON — Students in urban public school districts are less likely to graduate from high school than those enrolled in suburban districts in the same metropolitan area, according to research presented Tuesday.

The report by the Editorial Projects in Education Research Center found that about 75 percent of the students in suburban districts received a diploma, but only 58 percent of students in urban districts did.

The analysis of graduates in the 2003-04 school year examined U.S. Department of Education data from metropolitan areas surrounding the country's 50 most populous cities. Nationally, 52 percent of students in the main school districts of urban areas graduated.

The dropout rate of more than a million students each year "is not just a crisis; this is a catastrophe," said former Secretary of State Colin L. Powell, the founding chairman of America's Promise Alliance, which presented the research.

Secretary of Education Margaret Spellings said the government would soon require states to use a uniform method to report graduation data, although she did not provide specifics. This would require a change in the No Child Left Behind Act, which allows states to devise their own methods of determining graduation rates and tracking improvements.

"The problem is frequently masked by inconsistent and opaque data reporting systems," Spellings said. "For example, in some districts, a school only counts a dropout if you register as a dropout. ... In others, a dropout's promise to get a GED at an unspecified future date is good enough to merit graduate status. With these loose definitions ... it's no wonder why this epidemic is so silent."