Cara Delevingne was either targeted by an obsessed fan or a would-be thief -- either way, the end result was the same ... dude got caught red-handed thanks to an alert neighbor.

The incident went down around 11 AM Wednesday at Cara's L.A.-area home. Law enforcement sources tell TMZ, a neighbor called 911 to say they saw a man climbing over Cara's wall to her property.

We're told cops quickly responded, and their chopper spotted the man on the property ... while cops on the ground quickly surrounded the home. They ultimately found 22-year-old Sedric Ruempker on the property. Ruempker never made it inside the home, and was arrested for misdemeanor trespassing.

Our law enforcement sources say it's unclear if Ruempker randomly chose Delevingne's pad or if he was specifically targeting the actress. She was not home while all this was going down.