Check out this video, obtained by TMZ, which shows an older gentleman retreating with his hands up while being pursued by a Barstow PD officer Friday afternoon in the desert community. The cop has his baton raised as he inches closer, and eventually swings on him.

You can see the officer appear to give an order -- which looks like he might've been saying get on the ground -- before manhandling the older guy and subduing him. However, as the photog who took this noted, the cop starts to wail on the dude even after he's down.

He gets about 4 good swings on him before other officers arrive to the scene and help contain the situation. The man is then handcuffed and led over to EMTs, who briefly check him ... and he's then led to a police cruiser and taken away. The man can be seen limping.

Barstow PD tells TMZ the man who took the beating is 43-year-old Gary Christian -- whom they say was wanted on an open felony warrant for a probation violation ... and who this officer recognized on Main Street. BPD says the officer attempted to make contact and place Christian under arrest, but claim Christian assaulted the officer not once ... but twice.

BPD says the officer deployed his taser unsuccessfully, at which point ... the baton came out. They say Christian was treated at a hospital for minor contusions to his leg ... and was then booked into the San Bernardino County Sheriff’s Dept. High Desert Detention Center.

Barstow PD also says this ... "The department has a copy of that video and would like the community to know that a comprehensive administrative investigation will be conducted into this incident to determine if the force used by the officer was within Barstow Police Department policy and current law." In other words, they'll look into this internally.

Of course, the comparison to the beating Rodney King received in the '90s will undoubtedly be made. That incident led to destructive riots in and around Los Angeles -- and ultimately came to affect lots of other LA-based events in the years that followed.

The more concerning part about this, though, is that Barstow PD had another race-related police incident a few years ago ... when their officers shot and killed an unarmed Black in a parking lot as they felt an apparent threat. His name was Diante Yarber, a 26-year-old.

His family said the killing was unjustified ... but after a review by the authorities, they found the officers had a reasonable belief that their lives were in danger, and that deadly force was warranted. They fired around 30 bullets at his parked car, which was in a Walmart lot.

Considering the history in that town already, something tells us the community isn't going to take this latest incident very well. Fact is, it certainly looks to be excessive force on its face.