WASHINGTON

Seventeen of the nation's 50 largest cities had high school graduation rates lower than 50 percent, with the lowest graduation rates reported in Detroit, Indianapolis and Cleveland, according to a report released Tuesday.

The report, issued by America's Promise Alliance, found that about half of the students served by public school systems in the nation's largest cities receive diplomas. Students in suburban and rural public high schools were more likely to graduate than their counterparts in urban public high schools, the researchers said.

Nationally, about 70 percent of U.S. students graduate on time with a regular diploma and about 1.2 million students drop out annually.

"When more than 1 million students a year drop out of high school, it's more than a problem, it's a catastrophe," said former Secretary of State Colin Powell, founding chair of the alliance.

His wife, Alma Powell, the chair of the alliance, said students need to graduate with skills that will help them in higher education and beyond. "We must invest in the whole child, and that means finding solutions that involve the family, the school and the community." The Powell's organization was beginning a national campaign to cut high school dropout rates.

The group, joining Education Secretary Margaret Spellings at a Tuesday news conference, was announcing plans to hold summits in every state during the next two years on ways to better prepare students for college and the work force.

The report found troubling data on the prospects of urban public high school students getting to college. In Detroit's public schools, 24.9 percent of the students graduated from high school, while 30.5 percent graduated in Indianapolis Public Schools and 34.1 percent received diplomas in the Cleveland Municipal City School District.

Researchers analyzed school district data from 2003-2004 collected by the U.S. Department of Education. To calculate graduation rates, the report estimated the likelihood that a 9th grader would complete high school on time with a regular diploma. Researchers used school enrollment and diploma data, but did not use data on dropouts as part of its calculation.