(Adds farmer quotes, updates corn price, weather forecast)
By Ryan Schlader
CEDAR RAPIDS, Iowa, June 26 (Reuters) - More storms dumped crop-drowning rains on parts of the U.S. Midwest on Thursday, threatening strained levees and slowing recovery from a multibillion-dollar flood disaster in the heart of the world’s biggest grain and food exporter.
In Cedar Rapids, where 4,000 homes were flooded two weeks ago after water spilled over 1,300 city blocks, officials ordered 300 houses demolished. Efforts were under way to determine if some structures in the most flood-prone areas could ever be rebuilt.
The city asked federal disaster officials to send in 500 temporary housing units, most likely mobile homes of the type used following the devastation from Hurricane Katrina.
The National Weather Service said severe thunderstorms in already saturated areas of central Iowa would continue through Friday. Flash flood watches were in place for Des Moines, which saw serious floods two weeks ago, and other Iowa cities.
"A secondary threat of tornadoes is possible over eastern portions of central Iowa Friday afternoon," the NWS said.
Some estimates have indicated the recovery costs for Iowa flooding alone could exceed the $5.7 billion spent after the last major Midwestern floods 15 years ago in 1993.
Flooding from heavy rains that began in late May already have caused more than $6 billion in crop damage in Iowa, Illinois, Indiana, Missouri and Nebraska, the American Farm Bureau Federation, the largest U.S. farm group, said.
"I’ve been farming for 40 years now and this is probably the worst I’ve seen as trying to get a crop in the ground," said Gorin, Missouri, farmer Kenny McNamar. "It’s really going to put a hurt on a lot of people."
Fears that as much as 5 million acres (2 mln hectares) of corn and soybeans have been lost due to the flooding pushed corn and livestock prices to record highs last week.
On Thursday, Chicago Board of Trade corn for July 2009 delivery set another record high at $8.22 a bushel, more than double the 40-year average for corn prices. Corn is the main feed for meat animals, main source for ethanol fuel, and used in hundreds of other food and industrial products.
Iowa officials said this week that at least 2.5 million acres (1.01 million hectares) of corn and soybeans in Iowa, well above 10 percent of planted acreage in the top U.S. producing state for those crops, needs to be replanted. But it is too late in the season for good yields on replantings.
"It’s a bad situation. You can’t do anything," said Missouri farmer Jim Collins, whose 3,000 acres (1,215 hectares) of corn and soybeans sit about 50 miles west of the Mississippi River. "We’ll just have to try to collect on our insurance."
Worries about short supplies of basic food and feedstuffs have set off fresh alarms about rising world food price inflation even as oil and energy costs also set records.
The U.S. Federal Reserve cited rising inflation worries on Wednesday as it nervously kept U.S. interest rates unchanged.
Up to 5 inches (12.7 cm) of rain fell in parts of Iowa on Thursday and heavy rainfall was also reported in Missouri.
Additional heavy rains in the past two days have added new stress to levees along the Mississippi River north of St. Louis, though no new breaches were reported on Thursday.
"This is a dangerous time, and the longer the water stays up on the levee, the more dangerous it gets," said Alan Dooley, a spokesman for the U.S. Army Corps of Engineers in St Louis.
He said the prime area of concern is north of St. Louis on the Mississippi, including a levee at Winfield, Missouri, where a struggle has been going on for days to shore up an earthen berm protecting dozens of homes and a large chunk of farmland.
Patrick Slattery, a spokesman for the National Weather Service, said: "The thing about these storms right now is the ground is saturated and can’t absorb any more."
He said there is some hope that the additional rains will not have a major impact on the Mississippi though the additional water could prolong the flooding.
"Anything that falls in the flooded area is going to cause problems," he said. "It’s going to take a considerable amount of time for all of this water to leave," perhaps several weeks.
The Midwest storms and torrential rains have killed 24 people since late May. More than 38,000 people have been displaced from their homes, mostly in Iowa where 83 of 99 counties have been declared disaster areas. (Additional reporting by Carey Gillam in Kansas City and Erin Zureick in Chicago; Writing by Michael Conlon; Editing by Peter Bohan and Anthony Boadle)