Charlie Sheen's exclusive L.A. neighborhood is officially on lockdown -- TMZ has learned, the gated community where he lives literally QUADRUPLED security last week ... and it's all because of him.


Neighbors in the Mulholland Estates -- where Charlie lives -- tell TMZ, the Home Owners Association is paranoid about intruders snooping around Charlie's house ... so they've bumped the number of guards at the front gate from one to four.

But have you SEEN THE SIZE OF HIS HOUSE!? Forget a couple security guards -- damn thing needs its own military.