NEW ORLEANS (AP) - Hurricane Isaac pushed water over a rural levee, knocked out power and flooded beach-front roads in Louisiana and Mississippi early Wednesday as it began a drenching slog inland from the Gulf of Mexico with a newly fortified New Orleans in its path.

Wind gusts and sheets of rain pelted the nearly empty streets of New Orleans, where people watched the incoming Isaac from behind levees that were strengthened after the much stronger Hurricane Katrina hit seven years ago to the day.

Water driven by the large and powerful storm flooded over an 18-mile stretch of one levee in Plaquemines Parish south of New Orleans, flooding some homes in a thinly populated area. The levee, one of many across the low-lying coastal zone, is not part of New Orleans' defenses.

As the rain continued to fall and winds pushed across the Gulf Coast, it remained far too soon to determine the full extent of the damage.

Parish authorities believe some people may be trapped but were not sure how many may have remained despite an earlier evacuation. Rescuers were waiting for the strong winds to die down later in the day before moving out to search.

"We did have two parish police officers that were stuck in a car there. We just found out they were rescued and are safe," said emergency management spokeswoman Caitlin Campbell. Two other parish workers in a boat rescued them.

Isaac was packing 80 mph winds, making it a Category 1 hurricane. It came ashore at 7:45 p.m. EDT Tuesday near the mouth of the Mississippi River, driving a wall of water nearly 11 feet high inland and soaking a neck of land that stretches into the Gulf.

The storm stalled for several hours before resuming a slow trek inland, and forecasters said that was in keeping with the its erratic history. The slow motion over land means Isaac could be a major soaker, dumping up to 20 inches of rain in some areas, and every storm is different, said Ken Graham, chief meteorologist at the National, Weather Service office in Slidell, La.

"It's totally up to the storm," he said.

Isaac's winds and sheets of rain whipped New Orleans, where forecasters said the city's skyscrapers could feel gusts up to 100 mph.

Power was knocked out to 482,000 customers across southern Louisiana, about 157,000 of them in New Orleans, utility Entergy said.

In Mississippi, the main highway that runs along the Gulf, U.S. 90, was closed in sections by storm surge flooding. At one spot in Biloxi, a foot of water covered the in-town highway for a couple of blocks and it looked like more was coming in. High tide around 9:30 a.m. was likely to bring up more water.

In Pass Christian, a Mississippi coastal community wiped out by hurricanes Camille and Katrina, Mayor Chipper McDermott was optimistic Isaac would not deal a heavy blow.

"It's not too bad, but the whole coast is going to be a mess," he said early Wednesday.

McDermott stood on the porch of the $6 million municipal complex built after Katrina, with walls of 1-foot-thick concrete to withstand hurricane winds. As he looked out toward the Gulf of Mexico, pieces of a structure that had stood atop the city's fishing pier washed across the parking lot.

The state transportation department said Mississippi Highway 43 and Mississippi Highway 604, both in Hancock County, were not passable because of storm surge driven inland.

In largely abandoned Plaquemines Parish, Campbell said an 18-mile stretch along the thinly populated east bank was being overtopped by surge. The levee had not broken.

Campbell said officials believe some people may be trapped in their homes by water from the overtopped levee but were not sure how many might still be in the area. Strong wind was hampering efforts of rescuers to get into parts of the area.

She said officials expected the water to recede to the Gulf as wind direction changes with the storm's movement..

Tens of thousands of people had been told ahead of Isaac to leave low-lying areas of Mississippi and Louisiana, including 700 patients of Louisiana nursing homes. Mississippi shut down the state's 12 shorefront casinos.

The hurricane promised to lend even more solemnity to commemoration ceremonies Wednesday for Katrina's 1,800 dead in Louisiana and Mississippi, including the tolling of the bells at St. Louis Cathedral overlooking New Orleans' Jackson Square.

The storm drew intense scrutiny because of its timing __ coinciding with Katrina and the first major speeches of the Republican National Convention in Tampa, Fla., already delayed and tempered by the storm.

Isaac promises to test a New Orleans levee system bolstered by $14 billion in federal repairs and improvements after the catastrophic failures during Katrina. But in a city that has already weathered Hurricane Gustav in 2008, many had faith.

"I feel safe," said Pamela Young, who was riding out the storm in the Lower 9th Ward with her dog Princess in a new, two-story home built to replace the one destroyed by Katrina.

"If the wind isn't too rough, I can stay right here," she said, tapping on her wooden living room coffee table. "If the water comes up, I can go upstairs."

Isaac posed political challenges with echoes of those that followed Katrina, a reminder of how the storm seven years ago became a symbol of government ignorance and ineptitude.

President Barack Obama sought to demonstrate his ability to guide the nation through a natural disaster and Republicans reassured residents they were prepared Tuesday as they formally nominated the former Massachusetts governor as the Republican Party's presidential candidate.

There was already simmering political fallout from the storm. Louisiana's Republican Gov. Bobby Jindal, who canceled his trip to the convention in Tampa, said the Obama administration's disaster declaration fell short of the federal help he had requested. Jindal said he wanted a promise from the federal government to be reimbursed for storm preparation costs.

FEMA Administrator Craig Fugate said such requests would be addressed after the storm.

Obama promised that Americans will help each other recover, "no matter what this storm brings."

"When disaster strikes, we're not Democrats or Republicans first, we are Americans first," Obama said at a campaign rally at Iowa State University. "We're one family. We help our neighbors in need."

Along the Gulf coast east of New Orleans, veterans of past hurricanes made sure to take precautions.

Bonnie Chortler, 54, of Waveland, Miss., lost her home during Hurricane Katrina. After hearing forecasts that Isaac could get stronger and stall, she decided to evacuate to her father's home in Red Level, Ala.

"A slow storm can cause a lot more havoc, a lot more long-term power outage, 'cause it can knock down just virtually everything if it just hovers forever," she said.

Those concerns were reinforced by local officials, who imposed curfews in three Mississippi counties.

"This storm is big and it's tightening up and it sat out there for 12 hours south of us and it's pushing that wave action in and there's nowhere for that water to go until it dissipates," said Harrison County Emergency Operations Director Rupert Lacy.