By Curtis Skinner

SAN FRANCISCO (Reuters) - The former Stanford University swimmer, whose sentence for sexual assault has been widely condemned as too lenient, spoke of drug and alcohol use before entering college, undermining his claims to a judge that he lacked experience with alcohol, court documents showed on Friday.

Brock Turner, 20, was sentenced by Santa Clara County Superior Court Judge Aaron Persky to six months in county jail after being convicted of sexually assaulting an unconscious woman. Prosecutors had sought a six-year jail term.

In a letter to the judge before his sentencing, Turner said he did not have experience with alcohol. "Coming from a small town in Ohio, I had never really experienced celebrating or partying that involved alcohol," according to court documents.

He said in the letter that when he arrived at Stanford, he was encouraged by older members of his swim team and friends to drink during social situations.

"I wish I had the ability to go back in time and never pick up a drink that night," he said in the letter.

Court officials released numerous text messages sent and received by Turner that referenced buying and using marijuana and drinking alcohol before he entered Stanford, the court records showed.

In June 2014, Turner texted his sister about "raging" the previous night after spending an hour and a half drinking, according to court documents. That April, he discussed pooling money to buy marijuana with a friend, court records showed.

Turner's lawyer, Mike Armstrong, sent a text message to Reuters declining comment on the documents.

Uproar over the sentence was partially fueled by a letter from Turner's father to the judge that described the assault as "20 minutes of action," and a statement by the victim to the court detailing the January 2015 assault and its repercussions on her life. It is part of growing outrage over sexual assaults on U.S. college campuses.

At a Friday press briefing, when asked if President Barack Obama shared the anger expressed by Vice President Joe Biden in an open letter to the victim, White House spokesman Josh Earnest declined to comment on the case.

But, he said, "It is fair to say that the president feels strongly that every act of sexual assault and sexual violence and rape is wrong and one that deserves a forceful rebuke to make clear to everyone that we have certain principles and we have certain values in our country."

Officials have said Persky has received death threats since imposing the sentence, and he faces a possible recall effort led by a Stanford law professor.

Women's advocacy group UltraViolet said it would deliver on Friday a petition with more than 1 million signatures to the California Commission on Judicial Performance, an independent state agency, calling for Persky's removal from the bench. The group said it has hired a plane to fly over Sunday's Stanford graduation pulling a banner that will read, "Protect Survivors. Not Rapists. #PerskyMustGo."

USA Swimming, the U.S. national governing body for the sport, said Turner is not a member and would not be eligible in the future given his conviction, USA Swimming spokesman Scott Leightman said in an email. Turner's membership expired at the end of 2014, Leightman said.

USA Swimming prohibits and has zero tolerance for sexual misconduct, Leightman said.

Turner is due to be released on September 2 from the Santa Clara County jail. He was booked on June 2.

(Reporting by Curtis Skinner; Additional reporting by Suzannah Gonzales in Chicago and Doina Chiacu in Washington; Editing by Ben Klayman, Toni Reinhold)