Incessant thunderstorms dumped almost 12 inches of rain on Louisiana's bayou country yesterday, flooding homes and businesses and forcing evacuation of hundreds of people. One person in St. Martin Parish was killed when a car was swept off a road.

National Guard trucks were the only vehicles that could navigate the flooded streets and roads.

New Iberia was the center of the hard-hit area. Widespread flooding was reported throughout Lafayette, Vermilion, St. Martin and Iberia parishes, part of a region crisscrossed by bayous and canals near Louisiana's swampy coast. Gov. Edwin Edwards declared the four parishes a disaster area.

Snakes forced to higher ground by the rising water crawled into a public-housing project in Iberia Parish.

Although waters began receding during the day in some sections, the threat of more storms forced Vermilion Parish officials to order everyone out of the low-lying Erath area.

"They're predicting up to four inches more rain," said Vermilion Parish Sheriff Ray LeMaira. "If we get it, we've got real problems."

"When they say flash flood, they mean flash flood," said William Broome, 28, a teacher who took refuge in the National Guard armory in New Iberia. "There was no flooding, and then in just one hour it was 18 inches deep. . . . We'd open the door, and it would just wave in."

Five feet of water covered yards in the Orange Grove section of New Iberia.

"From the air, it's amazing," said Peter Piazza, a photographer who flew over the area. " . . . It looked like one giant rice paddy . . . . There are animals looking for high ground. The sugar cane fields are flattened."