Wal-Mart CFO: downturn difficult to predict

* "Difficult to say" how long economic downturn will last

* "Appropriately conservative" with forecast

* Share repurchases moderated as stock rises

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By Nicole Maestri

NEW YORK, May 13 (Reuters) - The U.S. economic downturn has "ingredients we haven't seen before," like the steep rise in gasoline prices, making it hard to determine how long the difficult climate will persist, the chief financial officer of Wal-Mart Stores Inc (WMT.N: Quote, Profile, Research) said in an interview on Tuesday.

"While we've seen gas prices go up historically, we've never seen the slope of the line -- that increase -- be so pronounced," Tom Schoewe told Reuters. "It's difficult to say how long this is going to last."

Schoewe made the comments after Wal-Mart, the world's largest retailer, reported a nearly 7 percent jump in first-quarter profits.