* Faces up to 15 years in prison when sentenced

* At issue "South Park" depiction of Prophet Mohammad in bear suit

* Extremists encouraged to attack the show's writers

By James Vicini

WASHINGTON, Feb 9 (Reuters) - A Muslim convert from New York pleaded guilty on Thursday for his role in threatening the writers of the satirical "South Park" television show for their depiction of the Prophet Mohammad and to other criminal charges, the U.S. Justice Department said.

It said Jesse Curtis Morton, who is also known as Younus Abdullah Muhammed, admitted his guilt at a federal court hearing in Alexandria, Virginia. He ran a website that encouraged Muslims to engage in violence against enemies of Islam.

Morton pleaded guilty to making threatening communications, using the Internet to put others in fear and using his position as leader of the Revolution Muslim organization's Internet sites to conspire to commit murder.

Morton worked on website postings with Zachary Chesser, a Virginia man who pleaded guilty in October 2010 to sending threatening communications to the writers of the comedy show and to other charges.

Morton, 33, was arrested in Rabat, Morocco, last year and brought back to the United States. He faces up to 15 years in prison when sentenced on May 18.

Morton admitted that he aided Chesser in taking repeated steps in April 2010 to encourage violent extremists to attack the South Park writers for the episode on the cable channel Comedy Central that featured Mohammad in a bear suit.

Most Muslims consider any depiction of the founder of Islam as offensive. Morton and Chesser posted where the writers resided and encouraged online readers to "pay them a visit," according to court documents.

Morton worked with Chesser to draft a message for the website about the South Park threats and they posted a final version of the statement on various extremist online forums.

Morton also conspired with Chesser and others to solicit the murder of an artist tied to the "Everyone Draw Mohammad Day" movement in May 2010, including posting online a magazine that included the artist in a hit list for violent extremists.

Four days after Chesser's arrest in July of 2010, Morton fled to Morocco. He was arrested in that country on U.S. charges in May last year and then sent back to the United States.

"Jesse Morton operated Revolution Muslim to radicalize those who saw and heard his materials online and to incite them to engage in violence against those they believed to be enemies of Islam," U.S. Attorney Neil MacBride said in a statement.

The case is USA v. Morton, No. 12-cr-35, in U.S. District Court for the Eastern District of Virginia.

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