Dennis Rodman -- unofficial ambassador to North Korea -- is celebrating his 54th birthday like a true dignitary ... with a MASSIVE PORN STAR BASH ... TMZ Sports has learned.

Three of the biggest porn stars in the biz -- Katie Morgan, Tasha Reign, and Teagan Presley -- will help The Worm blow out his candles at Sapphire gentlemen's club in Vegas on May 1st.

The club is gonna be insane that weekend -- not just because Rodman + porn stars = insanity ... but also because it's the weekend of the Mayweather/Pacquiao fight.

We're told Rodman and the X-gang will be hanging out in a private area of the club -- and guests can buy tix to enter for $250-a-pop.

As everyone knows ... Dennis loves birthdays -- just last year, he serenaded Kim Jong-un. No word if Mr. Supreme Leader plans to return the favor.