UPDATE 2-Carl Icahn steps down as adviser to U.S. President Trump

(Adds details on Icahn's investments, comment from ethics lawyer, request for comment from Icahn and White House)

Aug 18 (Reuters) - Billionaire investor Carl Icahn ended his role as a special adviser to U.S. President Donald Trump on Friday after facing criticism that his policy recommendations could help his own investments.

Some Democratic lawmakers and biofuels advocates argued that Icahn's policy recommendations to the Republican administration created a conflict of interest with his businesses, including oil refining company CVR Energy Inc. Icahn has denied any conflict of interest.

"I chose to end this arrangement (with your blessing) because I did not want partisan bickering about my role to in any way cloud your administration," Icahn wrote in a letter to Trump released on his website.

A call to Icahn's office and an email to the White House were not immediately returned.

Icahn's departure followed a flurry of changes at the White House. Trump on Friday fired his chief strategist, Stephen Bannon, two days after disbanding two high-profile business advisory groups.

The activist investor, who leads Icahn Enterprises LP , was an early and close ally of Trump who was often praised by the Republican for his business acumen. In his letter to Trump, he downplayed his role as an adviser, saying he "had no duties whatsoever." But his web of financial interests were a lightning rod.

"If he was not willing to admit he was a de facto special government employee, and follow the rules, then he had no place serving in government," said Norman Eisen, co-founder of Citizens for Responsibility and Ethics in Washington, who served as the chief ethics lawyer for former President Barack Obama.

"His short tenure, marred by serious conflicts allegations, was yet another black eye for an administration that has become notorious for violations of ethics and the rule of law."

Icahn has been one of the loudest critics of the federal biofuels program, and he was working at price-crushing reforms of the program at the same time he was betting that credits at the center of the program would fall.

Biofuels regulations require refiners either to blend biofuels into gasoline or - in the case of companies like CVR that have no blending facilities - to buy credits from competitors. The regulation, the Renewable Fuel Standard, also allows companies to delay those credit purchases by a year.

As an adviser to Trump, Icahn urged the president in February to alter the policy to lift the blending burden from refiners. Yet environmental regulators are preparing to formally reject that proposal, sources told Reuters.

(Reporting by Trevor Hunnicutt in New York and Jarrett Renshaw in Philadelphia; Additional reporting by Chris Prentice in New York and Valerie Volcovici in Washington; Editing by Sandra Maler and Tom Brown)