Lawyers for former Tom Albanese asked the court to dismiss the claim by the Securities Exchange Commission that he hid a $US3 billion ($A3.78 billion) writedown on Rio's Mozambique coal project in part because he relied on his underlings to make the decision.

While lawyers for the former chief financial officer of the $US100 billion miner, Guy Elliott, argued that Mr Elliott also relied on junior staff, while adding he was not an accountant by training to have the case dismissed.

The SEC charged Rio Tinto, Mr Albanese and Mr Elliott in October with fraud for allegedly inflating the value of its Mozambique coal reserves it acquired in 2011 for $US3.7 billion and sold just three years later for only $US50 million.

In a letter to the US District Court in New York, Mr Albanese's lawyers said the former executive relied on other staff to make the value assessment.

"The responsibility for the valuation impairment lay in the first instance with other employees and officers of Rio Tinto," the letter says.

The letter says Mr Albanese asked "hard questions" and trusted experts from a wide range of fields including accounting and operations.

"Mr. Albanese encouraged those who ran Rio Tinto Coal Mozambique to explore options to help the business to succeed and reasonably relied on Rio Tinto's specialists to make difficult valuation and impairment determinations in light of complex and constantly changing facts," the letter adds.

The letter claims that when Rio Tinto did announce the impairment, it was not material to investors and that he did not make any misstatements or omissions and that he did not behave recklessly as alleged.

Mr Albanese resigned in January 2013 after Rio Tinto announced a $US14 billion writedown on the company's aluminium and coal business, including the Mozambique impairment.

The SEC alleges the miner was in receipt of information regarding the project's much lower value in 2012.

The SEC alleges the fraud continued until a whistleblower reported it to the board in early 2013.

In a letter to the court, lawyers for Mr Elliott described the allegations by the SEC as "utterly false"

"The SEC takes snippets of documents out of context and tries to conjure a fraud out of a mere unsuccessful business venture. The allegations regarding Mr Elliott are fabricated," the letter says.

"As CFO, Mr Elliott, who is not an accountant by training, relied on a well-tested and rigorous process designed to ensure Rio Tinto's financial statements - including its balance sheet of over $US100 billion - were fairly stated and reported properly."

The letter added that the project itself was "exceedingly difficult to value" due to the it being in early development.

"That process began with executives in the business unit, who had first-line responsibility for analysing whether asset values should be reduced (or impaired)," said Mr Elliott's lawyers.

The letter also adds: "Even if there were misstatements or omissions, Mr Elliott did not make them."

Both sets of lawyers for the former executives also argued that neither Mr Albanese nor Mr Elliott stood to gain financially from the alleged delayed valuation downgrade.

For its part, Rio Tinto asked the court to dismiss the matter, saying the writedown was announced in a timely fashion.

It also argued that the writedown followed extensive feasibility studies by the company on the project.

Rio Tinto also told the court that it detailed in its 2011 annual report the highly risky nature of the Mozambique coal project.

"Rio Tinto's impairment decisions were reasonable because, among other things, its financial statements were never restated, and its independent auditor never withdrew its opinion on those statements."