President Obama will excuse states from key parts of No Child Left Behind, the federal education law, if they adopt certain education reforms in exchange for greater flexibility in deciding how to measure school performance.

The Obama administration offered the first details Thursday of the highly anticipated program, with as many as 45 states expected to participate.

States are chiefly interested in exemptions from a provision of the law that calls for every student to be proficient in math and reading by 2014, with the risk of escalating sanctions for schools that do not comply.

State officials and local educators call that goal unrealistic and its penalties unfair, and they have been clamoring for relief. Education Secretary Arne Duncan has said that by next year, more than 80 percent of schools across the nation will be labeled as failures under the law, although some experts dispute that figure.

In Virginia, where 40 percent of schools were considered failing under the law in 2010, state education officials said Thursday that they intend to seek a waiver. Maryland, where one-third of schools fell short in 2010, also plans to apply for a waiver, said William Reinhard, a spokesman for the state education department.

“We’re really, really looking forward to this,” Reinhard said. “It looks good. We take the requirements of NCLB very seriously and have no interest in turning our back on accountability. But for some of those schools that have been branded unfairly perhaps because a couple of kids missed . . . targets in some areas, this will get those schools out from under some unfair labeling.”

In the District, where 91 percent of schools failed to meet targets in 2010, officials have indicated interest in applying but have not made a final decision.

The administration plans a workshop next week to explain the program in detail to states, Reinhard said.

Senior administration officials said waivers will be awarded to states that adopt academic standards that ensure their high school graduates are ready for college or a career, measure school performance not merely by test results but by student improvement over time, and evaluate teachers and principals using a variety of measures, including but not limited to student test scores.

States will be required to launch “rigorous” campaigns to turn around their lowest-performing schools — the bottom 5 percent. And they will have to devise ways to focus on students with the greatest needs in another 10 percent of schools with low graduation rates or large achievement gaps between students of different races. States will also have greater flexibility with about $1 billion in funding for schools attended by poor children.

States will still be required to test all children in grades 3 through 8 and once in high school and report results by subgroups — including race, English learners and students with disabilities — so it is clear how every student is faring.

But Margaret Spellings, education secretary under President George W. Bush, said she worries about backsliding. “I’m skeptical about states’ ability or will to do great reform or close the achievement gap,” she said. “The reason this whole waiver issue is before us is [the states] told us they were going to do something and didn’t do it. And now they want a waiver against their own promises.”

“We need more accountability, not less,” Spellings added. “Implicit in this situation is the idea that it’s unreasonable to expect children to perform on grade level and we need to find a way to let the adults get out of that.”