WASHINGTON - The Department of Education said yesterday that school districts that lack space for children wishing to transfer out of failing public schools "must, to the extent practicable," forge cooperative agreements with other districts to accept those students. But federal officials said they would not scrutinize state plans to ensure such cross-district agreements were in place.

The announcement, which the department issued in draft guidance about the school transfer provisions of No Child Left Behind, reflects a more demanding stance on school choice among education department officials, who have until now spoken of encouraging, rather than requiring, agreements beyond district lines to accommodate children wishing to escape substandard schools. But it did not appear an intent to force the issue.

"The language is trying to send a message to parents at least as much as it is to school districts," said Eugene W. Hickok, the undersecretary of education. "Rather than talk about the enforcement, we're talking about the empowerment."

In final regulations issued two weeks ago, the Education Department said that all students in failing schools had the right to transfer to better schools in their district, regardless of overcrowding. School officials in some parts of the country have said that without sufficient resources, they could not see how they could supply children with better alternatives.

Some critics also maintained that the biggest disparity in educational quality is between school districts, not schools within a district, and that unless the law overcame that divide, its likelihood of delivering on the promise of leaving no child behind was small.

But practically, education advocates and analysts said, the demand for cross-district transfer agreements would be difficult, if not impossible, to enforce. The law leaves states and school districts to define what is "practicable," and the federal government would be unlikely to second-guess their judgments.

"That's a huge escape hatch," said Frederick M. Hess, a scholar in residence at the American Enterprise Institute. "The department would have to reject a district's determination of what's feasible and practicable. If it goes to enforcement, that's a difficult thing to show."

Given that enforcement is unlikely, education analysts and officials saw the department's tough new language on cross-district choice as signaling the primacy it is placing on monitoring efforts to satisfy the school choice provisions of No Child Left Behind.

"The administration's clearly indicating their priorities in implementing this law, and it has to do with choice and supplemental services provisions," said Ross Weiner, a principal partner at the Education Trust, which represents low-income, urban schools. "This is just another indication that this is what they're going to be paying attention to."