* One estimate pegs 300,000 to 600,000 tons delayed
* Both upstream, downstream terminals affected
* Exports expected to catch up after flood passes
(Recasts, adds detail, other comment; adds byline)
HOUSTON, May 24 Mississippi River flooding is slowing U.S. coal exports, with facilities for loading barges upstream and oceangoing vessels downstream both affected, companies said Tuesday.
Some 300,000 to 600,000 tons (544,310.8 metric tonnes) of coal, or four to eight shiploads, have been delayed so far, estimated Bruce Conti, president of Canadian National's (CNR.TO) IC Rail Marine Terminal.
"The river has had intermittent stoppages. It's significant. Things are just slower," added John Crane, vice president of St. James Stevedoring Co.
A spokesman for Kinder Morgan Energy Partners KMP.N said high water interrupted operations at several of its terminals upriver, but IMT export terminal downstream is unaffected.
Operators said they expected to recover from high-water delays after water recedes and not miss many, if any, deliveries.
Most U.S. coal exports flow from East Coast ports at Baltimore, Maryland, and in southern Virginia, but exports from the Mississippi River have been growing.
Analysts have predicted total U.S. exports this year will reach 100 million tons out of mine production totaling more than 1 billion tons. Most U.S. coal is burned domestically.
U.S. exports are experiencing a banner year because demand for coal is strong worldwide and other exporting nations have had bad weather or logistical problems with deliveries.
IC Rail Marine declared force majeure at its dock May 15, delaying two shipments totaling about 150,000 tons of coal headed for the United Kingdom, Conti said.
The terminal hopes to reopen the dock about June 1 and ship the delayed cargoes after that. Rail deliveries of coal to IC Rail Marine have not been affected, he said.
Most coal transshipped from the river to oceangoing vessels arrives by barge, and loading facilities upstream were shut early in the floods, slowing traffic, officials said.
St. James Stevedoring, a major mid-river transloader, has not declared force majeure but has had some ships delayed, Crane said.
Kinder Morgan's IMT export terminal, downriver from New Orleans, already was significantly slowed for shiploader repair and high water has had no effect, spokesman Joe Hollier said.
Kinder Morgan terminals upriver suspended dock operations due to high water, but landside work continues, he said.
"We don't expect a material impact," Hollier said.
(Editing by Sofina Mirza-Reid)