Fortifies L.A. Mansion with Firepower

... After Burglary Plot

LeBron James has beefed up security at his L.A. home in a major way -- bringing a team of armed guards to patrol his house after learning he was targeted by a team of burglars.

As we previously reported ... the LAPD arrested 4 people who had hit more than 24 homes of the rich and famous, including Yasiel Puig, Rihanna, Christina Milian and others.

Cops say the bad guys had a list of 12 more celebrity targets -- including LeBron, Matt Damon and Viola Davis.

We're told LeBron is taking the situation very seriously -- he's got a wife and 3 kids at home -- and is taking every possible measure to protect his family.

Sources tell us ... Bron has at least 10 armed security…