O.J. SIMPSON is furious with President Barack Obama for denying his request for a pardon, blocking what the fallen football hero felt was his best chance at winning his freedom, said an insider.

In desperation, O.J.’s law­yers have now launched a longshot bid by asking the Nevada Supreme Court to hear his appeal. His first ap­peal, to a lower court, failed.

Barring an unlikely Nevada Supreme Court hearing, ailing Simpson, 66, is facing at least three more years behind bars for his part in a bungled armed robbery in a Las Vegas hotel room. And he’s enraged at Obama for refusing him, said the source.

“Several months ago, O.J. wrote to Obama, ‘Mr. President, I know my life is coming to an end. Please, don’t let me die in prison,’ ” the insider told The ENQUIRER. “But O.J. has gotten word that Obama isn’t going to help him.”

Simpson claims that he instructed his legal team to soft-pedal his defense during his 2008 trial because he didn’t want to take attention away from

 Obama’s historic campaign to become America’s first African-American president, explained the source.

“O.J. feels Obama owes him and hoped Obama would intercede with his prison sentence,” said the insider.

Simpson was originally slapped with a nine- to 33-year sentence for a failed attempt to recover sports memorabilia he believed was stolen from him.

He’s behind bars at Nevada’s isolated Love­lock Correctional Center and will be eligible for parole in three years.

As The ENQUIRER has reported, Simpson also suffers from health problems, including an untreated brain tumor.

The insider said: “O.J. has told friends, ‘I really thought the president would help me. Now I feel the end is coming.’”