* Bush, McCain to visit flooded Iowa, aid debated
* 23 Mississippi River levees overflow so far
* Battle on to save rich farmland, cool food inflation
By Nick Carey
QUINCY, Illinois, June 19 (Reuters) - The Mississippi River surged past levees and spilled into farms, small towns and parkland on Thursday, adding to billion-dollar losses that have ignited global food inflation fears.
More than two dozen levees on the key U.S. commercial waterway have either overflowed or been breached, causing grain and meat prices to soar on concerns about short supplies.
Corn prices retreated early on Thursday, having set record highs for two weeks on flooding that has submerged or stunted crops on millions of acres (hectares).
Political pressure was growing to provide relief.
President George W. Bush will travel to Iowa on Thursday to survey flood damage in Cedar Rapids and Iowa City and meet with emergency workers and state and local officials.
Republican presidential candidate John McCain, an Arizona senator, will also be in the state to inspect the damage and the response.
His Democratic rival in the November presidential election, Illinois Sen. Barack Obama, visited earlier this week.
In Quincy, Illinois, along the Mississippi, the largely volunteer effort to fill and stack sandbags continued.
Jeff Steinkamp, chief engineer of Quincy, where the flooded river was expected to crest at 32.2 feet (9.8 metres) on Friday, said days of sandbagging levees had paid off so far.
"Everything is holding for now. So far, so good," he said.
The Army Corps, which operates river locks and dams, said 23 levees along the Mississippi had failed this week. It said 48 levees protecting more than 285,000 acres (115,335 hectares) of cropland from Dubuque, Iowa, to St. Louis, Missouri, were overflowing or at high flood risk.
The latest levee to be overtopped was close to the confluence of the Missouri and Mississippi rivers, north of St. Louis, that protected about 4,000 acres (1,619 hectares) of parkland. Another two-dozen levees are at risk of being swamped by floodwaters, the Army Corps said.
Levee breaches upstream temporarily lower the river’s level downstream.
‘A LITTLE RELIEF’
"We’ve had a little relief because the levee breaches lowered the river level a little. But it’s coming up again. We’re not done yet," said Kathy Dougherty of the Hancock County Emergency Services Agency in Dallas City, Illinois, north of Quincy.
Upriver, the U.S. Army Corps of Engineers reopened two locks as water levels receded. But locks along more than 200 miles of the vital commercial waterway remained closed to commercial traffic, stranding scores of barges.
The slow-rolling disaster, the worst flooding in the Midwest in 15 years, has swamped vast sections of the U.S. farm belt and forced tens of thousands of people from their homes.
The cost of the disaster may end up rivaling that of 1993 Midwest floods that caused more than $20 billion in damage and 48 deaths. Flooding and violent storms and tornadoes have been blamed for 24 deaths since late May. The damage has yet to be fully assessed.
Estimates are that 5 million acres of farmland across the Midwest have been ruined and will not produce a crop this year.
The prospects of smaller crops have jolted commodity markets, food producers and exporters. Chicago Board of Trade corn prices traded at a record $8.07 a bushel on Wednesday, but were down 8 cents on Thursday to around $7.92 a bushel. For 40 years, CBOT corn has traded mostly in a range of $2 to $4 a bushel. (Additional reporting by Lisa Shumaker in Chicago; writing by Andrew Stern and Peter Bohan; Editing by Vicki Allen)