By Jennifer Ablan and David Lawder

NEW YORK/WASHINGTON (Reuters) - Longtime Donald Trump supporter and activist investor Carl Icahn confirmed on Tuesday that the president-elect is looking at Wall Street veteran Steven Mnuchin as his choice for treasury secretary and billionaire Wilbur Ross for commerce secretary.

"Spoke to @realDonaldTrump. Steve Mnuchin and Wilbur Ross are being considered for Treasury and Commerce. Both would be great choices," Icahn wrote on Twitter.

Icahn, a close ally of Trump who was often praised by the Republican during the presidential campaign for his business acumen, also tweeted that both Mnuchin and Ross were friends and "two of the smartest people I know."

Mnuchin, a former Goldman Sachs partner and Trump's campaign finance manager, has been considered a front-runner for the Treasury post for much of the past week since Trump's stunning election victory.

Mnuchin's inclusion in Trump's campaign team was questioned at the time by Stephen Bannon, now Trump's chief White House strategist. In an interview on Breitbart News, Bannon asked Trump whether the then presidential candidate was "selling out to Wall Street".

The list to head the Treasury Department has also included JPMorgan Chase chief executive Jamie Dimon and Republican Representative Jeb Hensarling, chairman of the powerful House Financial Services Committee. Hensarling has said he would prefer to focus on a revamp of financial regulation, while Dimon, a lifelong Democrat, has denied interest in the job in the past.

Ross, a billionaire investor, is a part of Trump's economic advisory team. Calls to Ross were not immediately returned.

INTO THE TOWER

Mnuchin walked through the Trump Tower lobby in Manhattan on Tuesday morning. He would not comment on personnel decisions but said the Trump team is "making sure we get the biggest tax bill passed, the biggest tax changes since Reagan. So a lot of exciting things in the first 100 days of the Trump presidency."

With Republicans retaining majorities in Congress, Trump will have a clearer shot at enacting major tax cut and reform legislation and rolling back the 2010 Dodd-Frank financial regulation law passed in the wake of the financial crisis.

The new treasury secretary would play a key role in crafting such legislation, as well as managing potential new debt issuance of as much as $1 trillion if Congress agrees to Trump's proposed infrastructure spending program.

With such high stakes, Wall Street is more focused on the selection of the next treasury chief than it was during President Barack Obama's choices for the post.

“This time will be different,” Gregory Peters, senior investment officer at Prudential Fixed Income, said Tuesday at the Reuters Global Investment Outlook Summit in New York. “That role takes on greater importance.”

Unlike current Secretary Jacob Lew, who is viewed investors to have taken a lower profile focused largely on international issues over the past year, the next Treasury secretary is expected to be a featured player in articulating and executing the Trump administration’s new economic policies and initiatives.

A figure such as Mnuchin, with Wall Street experience, might be seen as better equipped to manage the relationship between Treasury and the banks that facilitate U.S. debt issuance.

The last Wall Street insider to serve in the post was Henry Paulson, the former Goldman Sachs CEO appointed by George W. Bush and whose term was dominated by the bank bailouts of the 2008 financial crisis.

Mnuchin, whose father was also a Goldman Sachs partner, worked at the investment bank for nearly two decades starting in the mid-1980s, a time when Wall Street was developing major financial innovations including new securitization techniques and collateralized debt obligations -- instruments that would later contribute to the financial crisis.

In 2009, he led a group of investors that purchased the assets of failed California-based mortgage lender IndyMac, for $1.55 billion that included a loss-sharing deal with the Federal Deposit Insurance Corp. After rehabilitating the operation and rebranding it as OneWest Bank, they sold it in 2014 for $3.4 billion to CIT Group Inc for $3.4 billion.

(Additional reporting by Emily Stephenson and Richard Leong in New York; Editing by David Chance and Alistair Bell)