WASHINGTON (Reuters) - The U.S. soldier convicted of providing secret files to WikiLeaks in the biggest breach of classified materials in the nation's history has asked for a presidential pardon, supporters said on Wednesday.

The request for Private Chelsea Manning, formerly known as Bradley, was filed by attorney David Coombs on Tuesday, according to a statement on the Pardon Private Manning website.

"I urge you to consider this matter closely and to take a positive step towards protecting whistleblowers who release information to the media for the public good by either reducing Private Manning's sentence to time served, or by granting him a full pardon," Coombs said in a letter to President Barack Obama via the Justice Department and to Army Secretary John McHugh carried on the website.

The application includes a supporting letter from Amnesty International.

A court-martial convicted Manning, 25, in July of 20 charges, including espionage and theft, for providing more than 700,000 classified files, videos and diplomatic cables to WikiLeaks, a pro-transparency website.

Manning was sentenced to 35 years in prison on August 21. The next day, the soldier issued a statement that said Bradley Manning was a female who wanted to live as a woman named Chelsea.

A psychiatrist at Manning's sentencing testified to having diagnosed the soldier as having gender dysphoria, or wanting to be the opposite sex.

Obama has received 1,496 petitions for pardons and 8,313 for commutation of sentence. He has granted 39 pardons and one commutation, according to the Justice Department's Office of the Pardon Attorney.

(Reporting by Ian Simpson; Editing by Scott Malone and Andrew Hay)