Edward Furlong -- Allegedly Exposed 6-Year-Old to Cocaine

Troubled actor Edward Furlong exposed his 6-year-old son to cocaine and should NOT be allowed to be near the child without strict supervision ... this according to court docs filed by his ex-wife ... but Eddie claims it's all BS.

Furlong -- who starred in "Terminator 2" and "American History X" -- appeared in court Friday to fight a court order which forbids him from being alone with his child.

FYI -- Furlong's custody rights had been severely reduced back in November after his ex-wife filed docs claiming the kid tested positive for cocaine after spending time with Edward. Furlong has a storied history of substance abuse.

But Friday in court, Furlong argued that his wife is a liar ... who will do or say whatever it takes to "alienate me further from my son and destroy my ability to work."

In the end, the judge didn't buy what Edward was selling -- and refused to change the custody restrictions already in place. During the hearing, the judge also expressed concern about his poor physical appearance.

Furlong has been on a downward spiral for years ... and was most recently seen wandering the streets of Skid Row in Downtown L.A.