When Hurricane Isaac whirled into the Gulf Coast this week, the federal levee system protecting New Orleans did its job. But the patchwork of floodwalls shielding subdivisions outside the city and rural fishing and farming communities was no match for the drenching storm.

As the cleanup began Friday, an old debate grew more urgent: Is it worth billions of dollars to build better levees in areas that are sparsely populated and naturally flood-prone?

Since Hurricane Katrina in 2005, the Army Corps of Engineers has backed away from the idea of extending protection across much of south Louisiana, citing doubts about whether improved levees would work and whether the money could be better spent elsewhere.

None of that sits well with locals, who feel abandoned.

"Each time you have a hurricane, you are going to spend enormous amounts of money on search and rescue, rebuilding churches, schools, everything, just like right here in Ironton," said Charles J. Ballay, district attorney of Plaquemines Parish, as he rode atop an airboat looking for stranded residents. "This was a Category 1 storm and look at what it has done."

The town baseball field was a lake, water lapped inside living rooms and children's toys bobbed in the high water. Not far away, ranchers tried to save a herd of cattle that stood neck-deep in the flood.

About 1 million people in coastal Louisiana live outside the massive levee system that protects greater New Orleans, and almost all of them are at risk of flooding during a major storm.

For decades, Louisiana has pressed the federal government to erect larger, stronger levees in areas vulnerable to hurricanes. The calls for better protection intensified after Isaac.

"These people don't deserve this," Democratic Sen. Mary Landrieu told WVUE-TV near Braithwaite, a community flooded to the rooftops when a nearby non-federal levee was overwhelmed by Isaac's storm surge. "We have to fight harder and stronger for protection for everyone. You know, on one side of the levee it's completely dry. Houses are safe. Families are going back to normal. And on the other side, it's a nightmare."

Matt Ranatza, a farmer in Jesuit Bend, a town left out of the federal system in Plaquemines, said the situation makes him "insane."

"There's a perfectly good levee right behind my house that they could have fixed, and that's the levee that was in danger of overtopping," he said. "For them to just say we're not going to do it there is criminal."

Huey Galmiche, an oil services salesman who evacuated to escape Isaac, said the parish was worth saving because it is a hub for the oil and natural gas industry. Anytime the main highway gets flooded, oil production is cut off.

"So that's costing us money for me and everybody that buys a gallon of gas, OK?" he said. "Raising the levee in the long run probably saves money."

Katrina killed about 1,400 people in New Orleans and caused flooding that covered about 80 percent of the city. The disaster exposed the corps' engineering standards as weak and unreliable, which led to revisions that made new levee systems even more expensive.

In the hurricane's aftermath, the corps was given $14 billion to protect New Orleans with new floodgates and floodwalls and higher levees. But none of those efforts encompassed the many smaller communities beyond the city, and the agency has struggled to offer those areas any added defenses.

In June, the corps scrapped plans to build a $1 billion levee system to protect areas between the Mississippi River and Bayou Lafourche southwest of New Orleans.

The agency said it could not find an economically feasible way to build levees or raise enough homes to guard parts of nine parishes against a storm with a mere 1 percent chance of occurring in any given year, also known as 100-year protection.

Meanwhile, another big-ticket levee project designed to protect Houma, the Morganza-to-the-Gulf project, is on hold because of similar doubts about costs and benefits.

At a news conference Friday, Landrieu said she hoped the levee issue would get the attention of Republican presidential nominee Mitt Romney, who was touring damaged areas.

She wanted Romney to see that the Corps of Engineers is underfunded.

"I realize that he's all about cutting the federal budget," Landrieu said. "But this is one agency that cannot, absolutely cannot, take any additional cuts."

For now, Louisiana is putting its hopes on money the state expects to get in coming years from increased offshore oil and gas royalties and other sources, such as money BP PLC is expected to pay for damage caused by its 2010 oil spill.

Still, even Louisiana has begun to second-guess the wisdom of trying to protect everything.

This year, the state issued a master plan that put emphasis on building so-called "ring levees" around towns and cities instead of erecting great wall-like systems to shield larger areas.

"We've drawn some lines in the sand," said Joseph Suhayda, a coastal oceanographic consultant. "There is a lot of area to protect, and the population density and property has got to factor in there somewhere."

But building levees takes time, and it's not clear that they are a reliable, long-term solution.

In Louisiana's poor soil conditions, levees sink and must be raised up every once in a while with new dirt. It can be costly to find suitable material to build them.

Besides that, the Louisiana coast is steadily eroding due to rising sea levels, oil drilling and even levee building that stops spring floods from replenishing marshes. The state has lost about 1,900 square miles of land since the 1930s, and scientists warn that more will follow.

Paul Kemp, a coastal geologist who heads the National Audubon Society's Gulf Coast Initiative, said many people in Louisiana are drawing back from the coast and behind the better levees systems.

"Look at Plaquemines since Katrina," Kemp said. "It has not been rebuilt. It's a bunch of trailers. That's what the future holds: People will have a house behind the levee and then have something more disposable outside the levees."