The judge’s ruling was a significant setback for the president, who had asserted broad authority to take executive actions in the face of congressional Republicans’ refusal to overhaul the immigration system. White House officials have defended the president’s actions as legal and proper even as his adversaries in Congress and the states have accused him of vastly exceeding the powers of his office.

In a decision late Monday, Judge Andrew S. Hanen, of Federal District Court for the Southern District of Texas, in Brownsville, ruled in favor of Texas and 25 other states that had challenged Mr. Obama’s immigration actions. The judge said that the administration’s programs would impose major burdens on states, unleashing illegal immigration and straining state budgets, and that the administration had not followed required procedures for changing federal rules.

Mr. Obama vowed Tuesday to appeal the court ruling and expressed confidence that he would prevail in the legal battle to defend his signature domestic policy achievement. “The law is on our side, and history is on our side,” he declared.

White House officials said the government would continue preparing to put Mr. Obama’s executive actions into effect but would not begin accepting applications from undocumented workers until the legal case was settled. That could take months. In the meantime, the president urged Republican lawmakers to return to negotiations on a broader overhaul of immigration laws.

“We should not be tearing some mom away from her child when the child has been born here and that mom has been living here the last 10 years minding her own business and being an important part of the community,” he said.

White House officials said the Justice Department was reviewing whether to ask an appeals court to block Judge Hanen’s ruling and allow the executive actions to proceed. But for now, the judge’s ruling could be a crushing disappointment to members of the immigrant community, who have spent much of the last two years pressuring Mr. Obama to act decisively to prevent deportations that separate immigrant families, including many with children or spouses who are living in the United States legally.

In Texas, Gov. Greg Abbott, a Republican who had filed the lawsuit in his former position as the state’s attorney general, hailed the ruling Tuesday as a victory for the rule of law. “President Obama abdicated his responsibility to uphold the United States Constitution when he attempted to circumvent the laws passed by Congress via executive fiat,” Mr. Abbott said, “and Judge Hanen’s decision rightly stops the president’s overreach in its tracks.”

Mr. Obama announced his executive actions on Nov. 20, shortly after Republicans won control of Congress. His plan to shield as many as five million undocumented immigrants from deportation immediately drew harsh attacks from conservatives and prompted legal challenges.

Under the judge’s ruling, the expansion of an existing program that was to begin on Wednesday will be postponed; for now, as many as 270,000 immigrants who came to the United States as children cannot apply for it. White House officials also said Tuesday that they were delaying a second program that would benefit about four million undocumented immigrants with children who are American citizens or legal residents. That program was scheduled to start in May.

Republicans in Congress seized on the judge’s ruling Tuesday to bolster their argument that funding for the Department of Homeland Security should not be approved without measures to block the president’s actions.

“The president’s extra-constitutional actions were rooted in political expediency and were devoid of a serious legal underpinning,” said Representative Trey Gowdy, Republican of South Carolina and chairman of the House Judiciary subcommittee on immigration. “This is not and never was about immigration law.”

But White House officials and some legal scholars noted that another federal judge had dismissed a different challenge to the president’s executive actions, and they predicted that Judge Hanen’s decision was likely to be suspended by the appeals court.

“Federal supremacy with respect to immigration matters makes the states a kind of interloper in disputes between the president and Congress,” said Laurence H. Tribe, a professor of constitutional law at Harvard. “They don’t have any right of their own.”

Immigrant advocates assailed Judge Hanen’s ruling, saying he had failed to consider the benefits to national security and the economy of having millions of unauthorized immigrants begin taking background checks and paying taxes. Activists said they would continue to prepare immigrants to file applications, on the assumption that the programs would soon be up and running.

“Detractors of these programs may try to paint this as a fight with the president, but make no mistake: Attempts to dismantle these programs are attacks on American families,” said Janet Murguía, president of NCLR, also known as the National Council of La Raza, the country’s largest Latino organization.

In his 123-page opinion, Judge Hanen said administration officials had provided “perplexing” misrepresentations of the scope and impact of the president’s actions. Calling the new programs “a substantive change to immigration policy,” he said they were, “in effect, a new law.”

As part of the president’s announcements on Nov. 20, the secretary of the Department of Homeland Security, Jeh Johnson, also established new priorities, instructing enforcement agents to concentrate on deporting terrorists, and gang members, as well as migrants caught crossing the border illegally.

The judge rejected the argument that those changes were a proper exercise of prosecutorial discretion, ruling that the administration had engaged in “a complete abdication” of enforcement. The Department of Homeland Security, he wrote, cannot “enact a program whereby it not only ignores the dictates of Congress, but actively acts to thwart them.”

White House officials said the judge’s order did not prevent Homeland Security officials from exercising that discretion, and they said the department would continue to focus its enforcement efforts on dangerous immigrants.

The ruling was not unexpected. In August, Judge Hanen accused the Obama administration of adopting a deportation policy that was “an open invitation to the most dangerous criminals in society.”

Since the lawsuit was filed on Dec. 3, the stark divisions over Mr. Obama’s sweeping actions have played out in filings in the case. Three senators and 65 House members, all Republicans, signed a legal brief opposing the president’s actions.

On the other side, a dozen states and the District of Columbia supported Mr. Obama.

Across the country, many immigrants were ready to fill out their applications when the immigration agency posted the forms for the first time on its website Wednesday.

Dulce Valencia, 19, who was born in Mexico but has lived almost all of her life in the United States, said she was disappointed that she would have to wait.

“I felt like my world crashed a little bit,” she said.

(Published by The New York Times - February 17, 2015)