By Jonathan Stempel

NEW YORK (Reuters) - Rio Tinto Plc (RIO.L)(RIO.AX) and two former top executives said civil fraud charges brought by the U.S. Securities and Exchange Commission over a failed African coal project are "plainly wrong" and should be thrown out.

In a court filing late Monday night, Rio Tinto, former Chief Executive Officer Tom Albanese and former Chief Financial Officer Guy Elliott rejected SEC claims they should have written down Mozambique coal assets no more than 11 months after buying them in 2011 for $3.7 billion (2.66 billion pounds), rather than waiting 17 months.

The delay enabled the big Anglo-Australian mining group to raise about $5.5 billion from U.S. investors kept in the dark about the deterioration, the SEC argued in a lawsuit filed in October with the U.S. District Court in Manhattan.

The defendants said that in the months after the acquisition they had reason to believe the value of the assets had actually grown by $1.2 billion, as rising prices for "scarce" coking coal helped offset lower barging and rail capacity.

The market viewed the eventual $3 billion writedown as immaterial "in the context of a company with total assets of about $120 billion," they also said, adding that the SEC did not claim that Rio Tinto's stock or bond prices were harmed.

"The SEC alleges that Rio Tinto should have taken the impairment within just 11 months of acquisition - at a time when Rio Tinto had not yet completed its analysis of the quantity and quality of available coal or determined whether there was a viable means for transporting that coal to market," the defendants said.

"The SEC is plainly wrong, and each of its claims consequently ... must be dismissed," they added.

U.S. District Judge Analisa Torres set a March 19 deadline for the SEC to respond.

Rio Tinto wrote off most of the assets, which it had acquired in a takeover of Riversdale Mining and later renamed Rio Tinto Coal Mozambique, in January 2013, and sold them in late 2014 for just $50 million.

The Monday filing came three days after the Australian Securities and Investments Commission brought its own civil court action against Rio Tinto, Albanese and Elliott over the coal assets.

(Reporting by Jonathan Stempel in New York; Editing by Jeffrey Benkoe)