Education Secretary Roderick R. Paige, who spearheaded implementation of the No Child Left Behind law, a centerpiece of President Bush's first-term domestic policy agenda, is stepping down, administration officials said yesterday.

The officials said that Bush will accept the resignation of Paige, 71, a longtime ally and former superintendent of schools in Houston who served as the nation's first black education secretary. They named White House domestic policy adviser Margaret Spellings as his probable successor.

If Paige's resignation becomes official -- which officials said is likely to happen next week -- he will be the third Cabinet member to leave since the election. Attorney General John D. Ashcroft and Commerce Secretary Donald L. Evans have also announced that they will not serve in a second Bush administration.

Paige, who got to know Bush in the early 1970s when they worked together on a community development project in Houston, is regarded as one of the most loyal members of the Cabinet. He traveled tirelessly around the country promoting the philosophy of No Child Left Behind, which aimed to introduce business-style accountability standards in primary and secondary schools.

For all the energy that Paige displayed in promoting the new law, many observers believed that real power over education policy lay in the White House, particularly with Spellings, who advised Bush on education issues when he was governor of Texas. Her promotion would be the second time Bush put a personal aide at the head of a Cabinet department. On Wednesday, Bush named White House counsel Alberto R. Gonzales to succeed Ashcroft.

Some conservatives expressed disappointment over the likely elevation of Spellings, interpreting it as a sign that the Bush administration does not plan any major new education initiatives in the second term. They would like the president to do more to promote alternatives to what they see as the failed public school system, particularly in urban areas, through greater use of vouchers and charter schools.

"I think the White House kept Paige pretty much under wraps," said William J. Bennett, who served as education secretary under President Ronald Reagan, and is a leading proponent of home schooling. "He wanted to talk a lot more about school choice, but they pulled the reins pretty tight on him."

Bennett said his preferred candidate for secretary of education would be someone like Eugene Hickok, the present deputy secretary, who made a big push for charter schools when he ran the Pennsylvania education system prior to joining the Bush administration. He also mentioned the Philadelphia schools superintendent, Paul Vallas, a Democrat who has won a nationwide reputation for repairing broken school systems.

While Bush administration officials insisted that Paige was leaving the administration of his own volition, others suspect that he may have been given a bit of a push. According to Chester Finn, president of the Thomas B. Fordham Foundation, a conservative education think tank here, Paige had earlier signaled that he still felt he had "some work" left to accomplish.

Finn described Paige as "a truth speaker" kept on a "very short leash" by the White House. "It would have driven me crazy," he said. "I would not have lasted four years with as little autonomy and authority as his team has had."

Paige, who attended segregated schools in Mississippi as a child, won headlines for his blunt warnings about the dumbing down of public education and the "achievement gap" between whites and African Americans. He promoted the No Child Left Behind law as a way to narrow the gap by holding students everywhere to the same standards and using the results of standardized testing as a way to reward good schools and penalize bad ones.

The secretary showed little patience with critics who argued that the law is too rigid and too bureaucratic to achieve its goals, and is likely to result in ever-increasing numbers of schools being dubbed "failures." In February, he caused a furor by describing the 2.7 million-strong National Education Association, the nation's largest teachers' union, as a "terrorist organization" for opposing No Child Left Behind. He later apologized for the remark.

Jack Jennings, a former Democratic congressional staffer who now runs the Center on Education Policy, said that the only major new education initiative on the horizon for Bush's second term was the extension of high-stakes testing to high schools. At present, No Child Left Behind focuses on testing in the third, fifth, and eighth grades.

"Bush is likely to be busy with Iraq, taxes and Social Security in the second term," Jennings said. "A new education secretary might carry more weight on Capitol Hill than Paige, but the policy itself is unlikely to change."

Don McAdams, who served with Paige on the Houston school board that pioneered many of the reforms that later became part of No Child Left Behind, said he was "not surprised" by the secretary's decision to step down after "four years in a very intense environment." He said that Paige had "several ideas for books," including one about the redesign of large urban school districts.

Education Secretary Roderick R. Paige promoted the No Child Left Behind law.