NEW ORLEANS — The U.S. economy faces losing billions of dollars in trade unless the Army Corps of Engineers’ budget for dredging the Mississippi River is increased to prevent the river from silting in, according to a new study commissioned by businesses that rely on the river.

Every year, the Corps keeps the channel open with dredges that remove mud and allow ships to get to the Port of New Orleans. But in the last year, the Corps has seen its dredging budget cut by about $45 million.

The new study — released Tuesday — warns that if the river silts in to the point where severe restrictions are imposed on the amount cargo ships can carry there would be a loss of $5.5 billion in exports and $3.7 billion in imports. The study was done by Tim Ryan, a Louisiana economist and former head of the University of New Orleans, on behalf of the Big River Coalition, a group of shippers, farmers, exporters, pilots and other businesses that rely on the river. The coalition is pressing Congress and the Corps to do more dredging.

The Mississippi is a major thoroughfare to the world’s markets for grain, soybeans, pig iron, coal and many other products for 29 states and Canada. About 60 percent of U.S. grain exports cross the mouth of the Mississippi. Between $85 billion and $104 billion in foreign trade passes through New Orleans, according to figures from the Customs and Border Protection.

In the Vicksburg District, seven ports and harbors on the Mississippi River are maintained through maintenance dredging: Vicksburg Harbor, Claiborne County Port, Madison Parish Port, Lake Providence Harbor, Greenville Harbor, Yellow Bend Port and Rosedale Harbor. Cutterhead dredges under contract to the Corps dredge the ports annually.

Also, the Dredge Jadwin, a four-story, 274-foot-long dustpan dredge built in 1933 and re-powered in 1985, clears silt from the river floor by a high-powered vacuum head.

But the river carries huge amounts of silt and sediment — about 200 million tons a year — and unless it is stirred up by dredges the river clogs up and that forces ships to reduce their draft. Draft is the depth of a loaded vessel’s keel below the water line.

The Corps, facing budget restraints like other federal agencies, last year set aside about $63 million for dredging efforts. Typically, the Corps had spent between $80 million and $100 million to keep the river open.

The Corps says it has set aside about $66 million this year for dredging on the lower river.

“Maintaining the deep draft of the Mississippi River is a priority for the New Orleans District because of its national implications,” said Rachel Rodi, a Corps spokeswoman.

At a news conference Tuesday, the Big River Coalition warned that unless the Corps’ dredging budget is increased, the draft on the river could be reduced from 45 feet to 38 feet. The study was based on a 38-foot-draft. Congress established a 45-foot draft as the proper depth for the river.

“I can’t understand why the federal government can’t get behind this productive river,” said Michael Lorino, president of the Associated Branch Pilots, a group of pilots that guides ships at the mouth of the Mississippi.

At the news conference, U.S. Rep. Charles Boustany, R-La., said he is pushing Congress to pass a bill to force the federal government to spend the money it collects through a national harbor maintenance tax on dredging and other channel work. Boustany faults the federal government for using only about half of $1.3 billion it collects a year in harbor maintenance taxes for dredging.