The LAFC team wants to KILL a soccer fan tradition of chanting a homophobic slur at players during goal kicks ... and says any fan who uses the word will be immediately banned from the stadium.

The threat came hours after the newest MLS expansion team played its first game at Banc of California Stadium on Sunday ... when they beat the Seattle Sounders 1-0.

During the game, fans could be heard chanting the word "p*to" -- a word that many people and organizations, including OutSports.com, have labeled a gay slur.

Now, the LAFC is laying down the gauntlet ... saying any fan who uses the word moving forward will get the boot.

"The offensive goal kick chant is wrong and not what we are about," team officials said in a statement.

"We ask that all of our fans and Supporters work to hold each other accountable to eliminate this from Banc of California Stadium."

"Any fans identified as participating in this offensive chanting will be removed from the stadium and the Club will revoke their season membership."