Justin Bieber -- My Killer Bodyguard ... Is Just A Big Puppy

Justin Bieber's bodyguard has been in a heated standoff with photogs and cops ... but he's just been given a tough new detail ... babying Bieb's 8 oz. puppy.

Biebs isn't playing around when it comes to Esther -- the same adorable little Silky Terrier he wined and dined at Mastro's in Bev Hills on Sunday ... it looks like he's put his top dog, Michael Arana, on the job.

The good news ... if Arana can handle himself against a gaggle of Miami cops or some unruly London paps like he did in 2013, he can more than handle picking up Esther's doodie.

No shame in taking care of the lil' doggie, as long as he's not getting paid in kibble.