* Mississippi River swamps towns, farms, crest near
* No new levee breaches, risks remain, East St Louis eyed
* Political pressure rising over faster aid, relief
PALMYRA, Mo., June 21 (Reuters) - The crest of the swollen Mississippi River moved relentlessly downstream on Saturday as volunteers manned sandbagged levees, nursed hopes and coped with the costs of the worst U.S. Midwest flooding in 15 years.
"At times like these you don't know whether to cry or laugh. But here in the Midwest we tend to favor the latter," said Charlotte Hoerr, who with her husband Brent farms land not far from the river in this small Missouri town.
The violent rush overcame more than two dozen levees this week, submerging small towns and vast stretches of prime farmland as the nation's most important river absorbed the runoff of torrential rains that put many Iowa towns under water last week. No levees were reported breached on Friday night.
The Midwest flooding and storms blamed for 24 deaths since late May have caused damage in the billions of dollars and are expected to push U.S. and world food prices higher.
Up to 5 million acres (2 mln hectares) may have been lost to just-planted crops at the heart of the world's top grain and food exporter. Prices for corn, cattle and hogs all set records this week due to the floods, as a world economy already slammed by inflation from soaring energy prices absorbed the blow.
The spillage onto the Mississippi's vast flood plain covered thousands of acres of crops. But several days of dry weather this week cut water flows, as did the levee breaches.
"It's starting to feel like the worst of the crisis has passed," said Farm Bureau official Blake Roderick in nearby Hannibal, boyhood home of author Mark Twain.
The river in Hannibal was expected to crest on Sunday at 28.7 feet (8.7 metres), below the record 31.80 feet (9.7 metres) set in the 1993 flood.
"We're still concerned that levees will be overtopped," said Ron Fournier, a spokesman for U.S. Army Corps of Engineers. "If the sandbags don't hold, there's going to be water in agricultural fields and residences."
EAST ST. LOUIS THREATENED
St. Louis, located 100 miles south and after the river widens considerably to more water, saw the river crest on Friday well below levels seen in the last major flood in 1993.
One worry was water seeping underneath levees from "sand boils," or leaks bubbling up from water pressure, across from St. Louis in the impoverished Illinois city of East St. Louis.
If the decades-old levees there failed, the river would spill onto a flood plain where 150,000 people live, said Timothy Kusky, a flood expert at Saint Louis University.
"Careful scrutiny of the levee system will continue until the river level falls," the St. Louis Army Corps said.
President George W. Bush toured some of the devastation in Iowa on Thursday, and the White House said relief would be made available from $4 billion in the government's disaster fund.
Bridges and highways have been swamped, factories shut down, water and power utilities damaged, and the earnings of railroads, farmers and myriad other businesses disrupted.
"Now we begin the process of assessing debris removal and short-term and long-term housing needs," said Bret Vorhees of Iowa Emergency Management. He said requests had declined for sandbags, water pumps, shelter and security.
Flood relief was rapidly becoming a political issue in an election year in the United States. Republican presidential candidate John McCain toured Iowa on Thursday, separately from Bush, while Democratic candidate Barack Obama helped stack sandbags earlier in the week in Quincy, Illinois.
"I've seen firsthand the growing magnitude of this flooding disaster, and unfortunately the end is not yet in sight," Illinois Gov. Rod Blagojevich said on Friday, saying he had asked Bush for faster aid for 20 flooded Illinois counties.
Don Rust, a farmer from Ursa, Illinois, not far from Quincy, estimated cropland 13 miles (21 km) long and six miles (9.7 km) wide was flooded in his area.
"It's a disaster, all right," said his wife Lisa, surveying the scene. "Welcome to the Midwest." (Additional reporting by Ros Krasny, writing by Peter Bohan, editing by Vicki Allen)
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