Ex-NFL superstar Clinton Portis says he loaded up a pistol in an effort to hunt down and KILL one of the people he blames for blowing his fortune ... but had a change of heart at the last minute. 

Portis says it all went down in 2013 ... he stalked an office building in Washington D.C. on several nights with the hopes of confronting one of the people who managed his money.

But Clinton wasn't looking for a fight -- telling SI.com, "It wasn't no beat up ... it was kill."

FYI, Clinton famously made more than $43 MILLION during his NFL career -- before losing it all through a combination of lavish spending and gross mismanagement by financial advisers. 

Some members of Portis' money team were punished by the NFL Player's Association and a federal regulatory agency for shady dealings -- but none of them went to jail for anything to do with Clinton. 

The ex-running back was pissed and wanted to take matters into his own hands.

But Portis says a call to a friend saved his life -- when she convinced him to holster his gun and think about his family. Portis says the thought of his 4 kids growing up fatherless ultimately convinced him to change his strategy.

Now, Portis says he's over his murderous anger -- and is focusing on growing his career as a member of the media.