According to law enforcement sources ... the suspect entered LL "s Los Angeles area house around 2AM, but unfortunately for him the actor/rapper/badass was home.

We "re told LL heard some commotion downstairs, went to check it out ... and found the intruder.

Sources say the intruder had tripped LL "s alarm system, but the "NCIS Los Angeles" star -- who is a physical beast -- decided to go hand-to-hand combat on the dude ... and managed to detain him until LAPD arrived a few minutes later to make the arrest.

We "re told LL is okay, but the suspect -- who will be booked for burglary -- suffered a few bruises.

Los Angeles Local News, Weather, and Traffic