WASHINGTON — The Justice Department has declared that President Obama can disregard a law forbidding State Department officials from attending United Nations meetings led by representatives of nations considered to be sponsors of terrorism.

Based on that decision, which echoes Bush administration policy, the Obama administration sent State Department officials to the board meetings of the United Nations’ Development Program and Population Fund in late spring and this month, a department spokesman said. The bodies are presided over by Iran, which is on the department’s terror list, along with Cuba, Sudan and Syria.

The administration’s decision was disclosed in a little-noticed legal memorandum recently posted on the Justice Department Web site.

The law at issue is a fairly narrow one, and presidents of both parties have long objected to such statutes as infringements on their power over foreign relations.

But assertions by the Justice Department that certain laws cannot bind the president have drawn far more attention since the Bush administration, when the Office of Legal Counsel wrote secret opinions authorizing the bypassing of statutes and treaties governing surveillance and the treatment of detainees.

John P. Elwood, who served in the Office of Legal Counsel in President George W. Bush’s second term, said the Bush team would probably have reached the same conclusion as the Obama officials about the United Nations statute. Nevertheless, Mr. Elwood said, “Any time you tell the president or an executive officer that it’s O.K. to disregard an act of Congress that is pretty explicit, I think that’s pretty significant.”

In the new opinion, David Barron, the acting head of the Office of Legal Counsel, wrote that the statute — a restriction Congress imposed in the State Department’s annual budget bill — “unconstitutionally infringes on the president’s authority to conduct the nation’s diplomacy, and the State Department may disregard it.”

His opinion cites many examples of previous administrations of both parties taking a similar view. Among them, Mr. Bush used signing statements to instruct the State Department to interpret identical restrictions as “advisory” rather than mandatory, and his administration sent officials to a Development Program meeting in January.

The chairwoman of the House appropriations subcommittee that oversees financing for the State Department, Representative Nita M. Lowey, Democrat of New York, strongly objected to the overriding of such statutes by the executive branch.

“This provision is law for a very good reason,” Ms. Lowey said. “There are consequences for being a state sponsor of terrorism. The decision of both the previous and current administrations to disregard this law is unacceptable.”

But Philip J. Crowley, a State Department spokesman, pointed out that the United States contributes about $400 million a year to the Development Program. It is in the national interest, Mr. Crowley said, to participate in meetings that will decide how to spend that money.

“We should not give Iran a veto over our national interest just because it happens to chair a particular meeting,” he said.

Nothing in the Constitution explicitly says Congress cannot forbid using taxpayer money to send certain officials to diplomatic meetings that lawmakers find objectionable. The Supreme Court has never ruled on the question.

“This is a realm of many questions and few answers,” said Harold H. Bruff, a University of Colorado law professor who worked at the Office of Legal Counsel in the Carter administration and is co-author of a casebook on separation-of-powers law.

Mr. Bruff, who is also the author of “Bad Advice: Bush’s Lawyers in the War on Terrorism”, said that while Mr. Barron’s memorandum authorized the president to bypass a statute, it was “considerably more nuanced and less sweeping” than some of the Bush team’s work.

For example, instead of claiming virtually exclusive power over foreign policy for the presidency, as some of the Bush legal team’s memorandums did, Mr. Barron’s opinion emphasized that Congress wields substantial authority over foreign affairs — even though this particular statute went too far, it argued.

Still, Curtis Bradley, a Duke University law professor who was a State Department lawyer in the Bush administration, said the new memorandum demonstrated that the Bush legal team’s approach was not as aberrational from other administrations as some critics contended.

Ms. Lowey and Senator Patrick J. Leahy, the Vermont Democrat who is chairman of the Judiciary Committee and the Senate subcommittee that handles State Department appropriations, criticized the administration for not telling Congress about its plans.

In a statement, Mr. Leahy said he recognized that “the current and former administrations may have legitimate constitutional concerns about this provision.” But he added: “There is no excuse for the administration’s failure to inform Congress that steps would be and in fact have been taken in violation of this provision. I cannot accept this.”

Justice Department officials pointed out that when Mr. Obama signed the legislation containing the provision in March, he issued a signing statement reserving a right to bypass any portions of the bill that restricted his power to conduct diplomacy.

Mr. Crowley acknowledged a failure to notify Congress about the decision to bypass the statute. “We probably could have done a better job keeping Congress informed,” he said, “but the law did not require any formal notification.”