WASHINGTON — The Justice Department urged a federal appeals court Monday to reinstate President Trump’s targeted travel ban, saying that a judge’s order blocking it endangered national security and violated the separation of powers.

Opponents of the ban have said it is a threat to the rule of law, to the nation’s security, and to the economy.

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With the filing of the administration’s brief, the challenge to the travel ban, the most ambitious and disruptive initiative of Trump’s young presidency, is ready for its most important judicial test yet, one that will yield the first appellate ruling.

Judges of the Ninth US Circuit Court of Appeals in San Francisco are to hear arguments Tuesday on whether the restraining order should continue.

The appeals court has refused to immediately reinstate the ban, and lawyers for Washington and Minnesota, two states challenging it, argued that any resumption would unleash “chaos’’ again, separating families and stranding university students.

The Justice Department responded that the president has clear authority to ‘‘suspend the entry of any class of aliens’’ to maintain national security. It said the travel ban was intended ‘‘to permit an orderly review and revision of screening procedures to ensure that adequate standards are in place to protect against terrorist attacks.’’

Trial judges around the country, including in Boston, have blocked aspects of Trump’s executive order suspending travel from seven mostly Muslim countries and limiting the nation’s refugee program, but none of those cases have reached an appeals court.

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And none of the lower-court rulings were as broad as the one under review in the case, State of Washington v. Trump. That ruling, from Judge James L. Robart, a federal judge in Seattle, blocked the key parts of Trump’s order. Robart’s ruling allowed immigrants and travelers who had been barred to enter the United States, and it inspired an attack from Trump, who accused the judge of endangering national security.

On Saturday, the administration asked the Ninth Circuit for an immediate administrative stay of Robart’s ruling without hearing from the plaintiffs. The court declined, instead asking for more briefs.

The appeals court’s order Saturday night was issued by Judge William C. Canby Jr., who was appointed by President Jimmy Carter, and Judge Michelle T. Friedland, who was appointed by Barack Obama. The third judge on the panel, Judge Richard R. Clifton, was appointed by George W. Bush.

Now that the requested briefs have been filed, a ruling from the appeals court should follow soon. It will almost certainly be appealed to the Supreme Court.

The two states’ appellate brief, filed early Monday, said Trump “unleashed chaos by signing the executive order.”

Other states have joined the fray. Hawaii, which had filed a separate lawsuit challenging Trump’s order, moved to intervene Sunday. The next day, 15 states and the District of Columbia filed a brief supporting Washington and Minnesota. Massachusetts was among them, along with California, New York, and Virginia.

“If this court were to grant a stay,” the supporting brief said, “it would resurrect the chaos experienced in our airports beginning on the weekend of Jan. 28 and 29, and cause harm to the states — including to state institutions such as public universities, to the businesses that sustain our economies, and to our residents.”

In a brief filed Saturday, the administration argued Robart’s order would cause irreparable harm to national security.

In response, lawyers for the two states said that was not plausible, as it would mean that the nation had long been suffering “some unspecified, ongoing irreparable harm.”

“That makes no sense,” the brief said. “As this court has held, preserving the status quo against sudden disruption is often in the interest of all parties.”

In the short term, it could prove difficult to find the necessary five votes at the Supreme Court to undo a lower court order; the Supreme Court has been at less than full strength since Justice Antonin Scalia’s death a year ago. The last immigration case that reached the justices ended in a 4-to-4 tie.

But the travel ban
expires in 90 days, meaning it could run its course before a higher court takes up the issue. The administration could change it in any number of ways that would keep the issue alive.

The Supreme Court bench also could be full, with a new ninth justice on board, by the time the court is ready to hear arguments. If Judge Neil Gorsuch, Trump’s nominee for the court, is confirmed this spring chances of a tie vote would disappear.

On Saturday, the administration urged the Ninth Circuit to reject arguments based on religious bias, even though Trump has said he meant to favor Christian refugees. Judicial consideration of the president’s motives, the administration’s brief said, would violate the separation of powers.

Washington and Minnesota said “courts have both the right and the duty to examine defendants’ true motives.”

They added that the administration had taken “a dizzying number of positions” on whether the executive order applied to permanent residents holding green cards. The order appears to cover such people, but the administration has said it won’t enforce that part of the order.

Questions about permanent residents are not moot, the states said; the administration could again change positions.

Massachusetts Attorney General Maura Healey joined a coalition of 16 attorneys general in filing a brief in
San Francisco opposing the immigration ban. The attorneys general of 15 states and the District of Columbia argued Trump’s order would have an adverse effect on the states as well as the interests of each state’s residents and institutions, such as universities and businesses whose students and employees would be affected. “We now all stand together in facing concrete, immediate, and irreparable harms from the executive order,” the states argued.

Healey said Monday that “no president or administration is more powerful than our laws and our Constitution. As state [attorneys general], it is our job to hold this administration accountable and stand for the interests of our states and our residents.”

Several former diplomatic and national security officials filed a declaration against the ban Monday, including John Kerry, secretary of state under Obama, and Madeleine Albright, who had the position in the Clinton administration.

“We view the order as one that ultimately undermines the national security of the United States, rather than making us safer,” the declaration said.

After the Seattle court ruling, the State Department said people from the seven countries — Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen — could travel to the United States if they had valid visas.

Milton J. Valencia of the Globe staff contributed to this report.