(Updates with mandatory evacuation of Cairo, Illinois)
CHICAGO, April 30 (Reuters) - A U.S. government agency moved a step closer on Saturday to blowing up a Mississippi River levee to control flooding after a court decision cleared the way for it to proceed.
U.S. Army Corps of Engineers officials said they dispatched barges to the Birds Point levee near Cairo, Illinois, carrying a slurry mix that could be used to detonate the levee. The barges are set to arrive at Cairo from Hickman, Kentucky, late on Saturday.
"That is one of the many decisions that we make before and if we ever get to the decision (to detonate)," Major General Michael Walsh of the Army Corps told reporters.
"After that, the next decision is to take the barges and preposition them. The next one is to charge the pipes and the next one is to operate (detonate)," he added.
He provided no timetable for the decisions and said the Corps was closely watching river levels, expected to crest by Tuesday.
A federal appeals court said earlier on Saturday the Corps had the right to breach the levee to prevent flooding in Cairo, as permitted by a 1928 law.
Cairo, a historic town of 2,800 people, is at the confluence of the Ohio and Mississippi Rivers. Both rivers have been rising as a result of days of rain and the melt and runoff of the winter's heavy snowstorms.
The state of Missouri originally sued to stop the Corps plan, arguing that blowing up the levee would flood 130,000 acres (52,000 hectares) of Missouri farmland and do extensive damage. The states of Illinois and Kentucky took the other side, saying that towns in their states could be flooded if the levee were not blown up.
A lower court ruled against Missouri on Friday, and the state then petitioned to the U.S. Circuit Court of Appeals.
"I'm pleased that the court quickly rejected Missouri's request. The Army Corps must have the ability to take any action necessary to protect lives and homes in Cairo and the surrounding communities," Illinois Attorney General Lisa Madigan said in a statement.
The Corps said it would detonate explosives in the levee if the river at Cairo reached 61 feet (19 metres) and was rising. But it could potentially blow the levee even if the river does not reach 61 feet if there is too much stress on the system.
The river, at 59.2 feet (18 metres) on Saturday afternoon, is forecast to rise to 60.5 feet (18.4 metres) by Tuesday, according to the National Weather Service.
Cairo Mayor Judson Childs late on Saturday ordered a mandatory evacuation of the city as of midnight CDT (0500 GMT), the Corps SAID.
In Missouri, some 230 residents have been evacuated and the National Guard has set up command posts, the governor said. (Reporting by Christine Stebbins, Editing by Greg McCune)