The Justice Department “stands strongly behind the opinion, which is narrowly drawn and carefully reasoned,” Erik Ablin, an agency spokesman, said in an e-mail message. “Most of the criticisms that have been outlined against the opinion are thoroughly addressed in the opinion itself. Each of them lacks merit.”

Carl H. Esbeck, a University of Missouri law professor and architect of the religion-based initiative movement, also defended the opinion, saying the Religious Freedom Restoration Act compelled the department’s conclusion. “I understand that liberal law professors don’t like this,” he said. Why, he asked, should World Vision “be denied the opportunity that everyone else has to compete for funding simply because of their religion?”

The Office of Legal Counsel issues interpretations of the law that are binding on the executive branch and often rules on matters that are difficult to get before a court. Under the Bush administration, it has drawn sharp criticism for issuing opinions that provide legal cover for controversial policies preferred by administration officials.

In 2002, for example, the office secretly signed off on the use of harsh interrogation techniques despite a statute and treaties forbidding torture. The memorandum’s legal reasoning was strongly criticized by legal scholars after it was leaked to the public, and the Justice Department rescinded it.

Christopher E. Anders, senior legislative counsel to the American Civil Liberties Union, said he was alarmed by the 2007 memorandum’s conclusion that the government does not have a “compelling interest” in enforcing a federal civil rights statute.

“It’s really the church-state equivalent of the torture memos,” Mr. Anders said. “It takes a view of the Religious Freedom Restoration Act that allows religious organizations to get federal funds without complying with anything.”

Professor Lupu did not go that far, but said the opinion made “an aggressive reading of ‘substantial burden’ in a way that is not consistent with what courts and other agencies have done in the past, and it is designed to serve the president’s political agenda.”