Seth MacFarlane Rejects Porn Awards -- I Can't Find an Opening

Seth MacFarlane is officially OUT as the host of Hollywood's most prestigious award show ... the AVNs ... which means he will no longer get the chance to present the 2013 award for "Penis of the Year."

The Adult Video News awards -- kinda like the Academy Awards of XXX -- had reached out to MacFarlane, hoping he would front the 2013 award show ... since he's been on a hosting tear lately, with 2 Comedy Central Roasts under his belt and an upcoming gig at the Oscars.

In a letter to Seth's agents, the AVN people called him the "ideal host" ... and hoped he would follow in the footsteps of past hosts like Lisa Lampanelli.

But a rep for MacFarlane tells TMZ, the "Family Guy" honcho simply won't be able to rise to the occasion 'cause he's "a little busy right now."