NEW ORLEANS — Since the first days after Hurricane Katrina, when the streets were still under water, many residents of New Orleans and its surroundings have maintained that the flood that wrecked their lives was the government’s fault, and that the government should pay for it.

On Wednesday night came news that many had hoped for but few had believed would ever actually happen: a federal judge agreed.

“My head is spinning,” said Pam Dashiell, a co-director of the Lower Ninth Ward Sustainability Project and a 20-year resident of the neighborhood. “Maybe things are really breaking for the people.”

The sense of vindication was widespread, but the practical implications were less clear. The morning after Judge Stanwood R. Duval Jr.’s decision that the Army Corps of Engineers’ negligent maintenance of a major navigation channel led to major flooding in the Lower Ninth Ward and the adjacent St. Bernard Parish, a pleasantly startled New Orleans was still trying to decipher what it meant.

Was it an opening for tens of thousands of lawsuits, or a big class-action lawsuit, that could add up to billions of dollars in compensation for residents? Or was it leverage for negotiating a broader, regionwide settlement with the government? Some experts suggested that it was a welcome but ultimately symbolic ruling that could be overturned on appeal.

Charles S. Miller, a spokesman for the Department of Justice, said that the government was still reviewing the decision.

“We have made no decision as to what the government’s next step will be in this matter,” he said in a statement.

But given the potential of liability, legal experts are expecting the government to appeal.

The United States Court of Appeals for the Fifth Circuit in New Orleans, where the case would go, has a record of hostility to plaintiffs in environmental cases, said Oliver Houck, a law professor at Tulane University. But, he said, Judge Duval’s decision is so technical and packed with details — it came with a 33-page appendix of graphs, charts and maps — that there are only a few areas where it would be exposed to a reversal.

“For an appellate court to reverse him on the facts is unthinkable,” Professor Houck said.

In 2008, Judge Duval dismissed a lawsuit arising from drainage canal breaches that flooded much of the city, ruling that a 1928 act gave the corps immunity for damages that came from a flood protection project. But his decision was scathing nonetheless, and he insisted that the government should not be free “from posterity’s judgment concerning its failure to accomplish what was its task.”

Wednesday’s decision was about a different corps project, the Mississippi River-Gulf Outlet, a navigation channel known as MR-GO (pronounced Mister Go). In the 156-page decision, the judge wrote nearly as much about complicated immunity issues as he did in determining that the corps’s negligent maintenance of the channel actually caused the flooding in two areas, including the Lower Ninth Ward.

Lawyers for the corps had raised a variety of immunity shields in addition to the Flood Control Act, and the judge knocked these down one by one. With every one, though, he created a potential opportunity for higher judges to overturn the decision on appeal.

The judge ruled that the corps was liable for damages because, he said, it should have been filing environmental impact statements as the landscape around the channel significantly changed: wetlands had disappeared, levee banks had eroded, and the channel had more than doubled in width.

This is a conclusion of law rather than of fact, experts said, and thus is open territory for appeals judges. When legal opinion is at issue, said Howard J. Bashman, a Pennsylvania lawyer specializing in appellate practice, “the court gets to make up its own mind, without any deference paid to the trial judge in how the law was applied.”

At a Thursday morning news conference, the plaintiffs’ lawyers painted the decision in superlative terms, even comparing it to the victory over the British in the Battle of New Orleans.

The lawyers said they hoped the decision, and the possibility of thousands more cases following, would compel Congress and the Obama administration to agree to some kind of larger settlement for the entire city, like the one for victims of the Sept. 11 attacks.

“It’s time that we stopped litigating and started negotiating,” said Pierce O’Donnell, one of the lead lawyers.

Mr. O’Donnell said that he and the other lawyers had scheduled meetings on Capitol Hill in the coming weeks at which they would push for damage compensation for property owners, billions of dollars to rebuild infrastructure projects, and restoration of the area’s coastal wetlands. They will also demand a widespread overhaul of the Army Corps.

For now, however, much of the city was just enjoying a rare sense of triumph. Friends who were watching the news Wednesday night grabbed for their cellphones. At a coastal planning meeting in St. Bernard Parish, people broke into applause.

Mark Madary, who was on the St. Bernard Parish Council at the time of Hurricane Katrina, had campaigned against MR-GO ever since he heard the forecasts of catastrophe at a sportsmen’s league meeting in 1978. He said he never thought the case would even make it to court, but now expects a regionwide settlement.

“Now that the corps has been thrown over and exposed, it’s their duty,” Mr. Madary said.

Others in New Orleans, a city that has become accustomed to disappointment over four long years, were not as elated.

“It is an answer to something that was obvious from the beginning, and we’re glad we finally got a federal judge to agree with us,” said Robert Green Sr., a resident of the Lower Ninth Ward, who lost his mother and granddaughter in the flooding.

But it was clear that Mr. Green was more interested in talking about a grocery store that could be coming to the neighborhood.

“The lawyers are happy and the people are happy,” Mr. Green said of the decision. “But at the same time, we waited four years. So you deal with the important issues that are right in front of you.”

Copyright 2009 The New York Times Company