The Mississippi River's crest rolled downstream on Friday, submerging small towns and some of the U.S. Midwest's most fertile farm fields with a relentless flow as people and industry struggled to cope with the effects of the worst flooding in 15 years.

The flooding and violent storms blamed for 24 deaths since late May have generated damage in the billions of dollars and are expected to aggravate rising food prices.

Hannibal, Missouri, the boyhood home of author Mark Twain, was dry behind its earth levee and flood wall but other towns on both sides of the engorged river were not so lucky.

It's starting to feel like the worst of the crisis has passed, said Farm Bureau official Blake Roderick in Hannibal.

The Mississippi River breached or overtopped more than two dozen levees this week, including two reported as overtopped on Friday. At least a half-dozen others were still seen at risk as it crests above St. Louis, Missouri, through Sunday.

Most of the levees protect huge areas of prime crop land, including thousands of acres in Iowa and Illinois -- which together produce about one third of the U.S. corn and soybean crops -- that have been lost to flooding. That has sent shock waves through commodity markets and raised inflation concerns.

Don Rust, a farmer from Ursa, Illinois, estimated cropland 13 miles long and six miles wide was flooded in his area.

It will take three to four months for this water to recede, Rust said, looking over flooded fields. This is a lot of good land that will be useless until next year.

LEVEE WORRIES PERSIST

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.

Floodwaters have swamped farms and homes north of St. Louis, though the city itself appeared to be safe. The river widens there and can absorb much greater volume of water.

Harvey Johnson, deputy administrator of the Federal Emergency Management Agency, told reporters on Friday: The water is still rising in some places in Wisconsin. But it's cresting at levels below the anticipated predicted area in St. Louis and East St. Louis.

The Army Corps said it now expected the river in St. Louis to crest on Friday at 37.3 feet, compared to the record of 49.58 feet in the July, 1993, flood.

Still, water was seeping underneath levees across from St. Louis in the impoverished Illinois city of East St. Louis.

If the decades-old levees there failed -- and the Army Corps said two weeks ago the earthen structures need to be replaced -- the river would spill onto a flood plain where 150,000 people live, said Timothy Kusky, a flood expert at Saint Louis University.

He said that over the years, the Mississippi has been hemmed in by more and more levees, giving it less area to spread out. Where it does break through, the flooding is worsened.

DAMAGE ESTIMATES SURE TO RISE

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.

Barge traffic remains halted on the mid-Mississippi River, costing barge carriers millions of dollars a day.

Insurance companies that sell crop coverage to farmers, including market leader Ace Ltd., could face claims of as much as $3 billion in Iowa alone, a Lehman Brothers analyst said.

Claims from homeowners may not be large because few have flood insurance, industry analysts said.

The flooding in five Midwest states was thought to have ruined at least 5 million acres of cropland.

Corn prices have retreated since hitting records above $8 a bushel this week at the Chicago Board of Trade. But cattle and hog prices set record highs again on Friday, as feed costs soar and farmers consider cutting herd sizes.

Any significant rainfall -- or a summer drought -- could cause grain prices to take off again, traders said.

Since the United States is the world's biggest grain and food exporter, the rising domestic food inflation is sure to aggravate global prices in coming months, analysts said.

After several days of mostly rain-free weather in hard-hit Iowa, rivers retreated and left behind a clean-up mess.

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.

Nearly 4,000 homes in Cedar Rapids were damaged or ruined, Vorhees said.