In the blueprint for overhauling federal education policy that President Obama sent to Congress on Monday, his administration seeks to confront some of the major educational challenges that have developed during the eight years that President George W. Bush’s No Child Left Behind law has been a powerful influence on the nation’s public schools.

The administration’s proposal, if enacted into law, would encourage states to raise academic standards after a period of dumbing-down, end the identification of tens of thousands of reasonably managed schools as failing, refocus energies on turning around the few thousand schools that are in the worst shape and help states develop more effective ways of evaluating the work of teachers and principals. And those are just some of its goals.

But this ambitious agenda presents striking challenges of its own, both political and in terms of implementation.

Teachers’ unions and some Republican lawmakers immediately signaled their dislike for pieces of the plan, complicating the administration’s job as Congress takes up the task of reworking the No Child law. And even if lawmakers were to adopt the plan in its broad outlines, experts said, years of work would be required to roll out the new federal policies to states and in the nation’s 15,000 school districts.

“This would require an immense reorganization of American education,” said Amy Wilkins, a vice president at the Education Trust, an advocacy group that works to close achievement gaps between minority and white children.

The administration’s blueprint, for example, calls on states to adopt new academic standards that build toward having all students ready for college and career by the time they leave high school. The National Governors Association introduced a draft of new standards that fit that description last week, and many states appear likely to adopt them. But even if the vast majority of states do so, that adoption process is likely to take a year or so, and the new standards will require a new effort to retrain teachers, develop new textbooks and write new tests.

The administration’s testing proposals themselves represent a big new challenge.

The standardized tests developed by the states under the No Child law focus on measuring the number of students in each grade level in each school who are proficient in reading and math. Now the administration would like to shift the focus to measuring each student’s academic growth, regardless of the performance level at which he starts.

Many educators consider that shift a promising one, but fewer than half the states currently have the advanced student data tracking systems needed to measure student academic growth. And experts say it could take several years for all states to develop those systems.

“These are all big challenges,” said Jack Jennings, a former Democratic Congressional staff member who is president of the Center on Education Policy, a research group. “But in my view the administration has put forward a thoughtful proposal for dealing with several of the worst problems created by No Child Left Behind.”

Some Republican analysts were also impressed.

“It’s a serious blueprint, and one that would be a huge improvement over current law,” Michael Petrilli, a vice president at the Thomas B. Fordham Institute who served in George W. Bush’s Education Department, wrote in his blog. One feature he liked, Mr. Petrilli said, was that the blueprint would “focus most of its muscle and prescriptiveness on a handful of the worst schools.”

The current law requires that test scores increase in every school every year, to meet the requirement that 100 percent of students reach proficiency by 2014. According to a new research report by Mr. Jennings’s center, 31,737 of the 98,916 schools missed the law’s testing goals last year, vastly more than any level of government can help to improve.

The administration’s blueprint would refocus the most energy and resources on about 5,000 truly failing schools, and it outlines several models for how districts could intervene in them. Most would involve dismissing the principal and many teachers.

Teachers’ unions criticized those models.

“It’s just not a solution to say, ‘Let’s get rid of half the staff,’ ”said Dennis Van Roekel, president of the National Teachers Association. “If there’s a high-crime neighborhood, you don’t fire the police officers. This is a huge issue for us.”

Representative John Kline of Minnesota, the ranking Republican on the House education committee, said the blueprint “identifies many of the right goals for improving our schools.” But Mr. Kline said he questioned many of its proposals, “particularly those that increase federal intrusion.”

Grover Whitehurst, a senior fellow at the Brookings Institution, who headed the Education Department’s research wing during the Bush administration, noted that while the No Child law ran to 600 pages, the blueprint is only 41, outlining general goals but omitting myriad details.

“As the administration reveals those details, more political difficulties and implementation difficulties will arise,” Mr. Whitehurst said.