Brooke Mueller -- Don't Test Our Twins for Fetal Alcohol Syndrome ... PLEASE!

Brooke Mueller is desperately trying to stop a test that could show her substance abuse caused serious damage to her twin boys ... so claims the twins' father, Charlie Sheen.

Sources connected to their custody war tell TMZ ... Brooke had agreed to have Bob and Max tested for Fetal Alcohol Syndrome (FAS), but at the last second she did an about face and filed legal docs to block the test.

Brooke claims the kids are fine, so there's no need for a test.

Charlie vehemently disagrees, claiming the kids have real issues and an FAS test could help in the treatment.

TMZ broke the story ... Denise Richards told DCFS Bob and Max tortured the family dog and viciously attacked her two daughters, strangling and punching them ... even throwing feces at one of them. And the kids were violent at school, hurting other kids and punching a teacher in the face

Charlie and Brooke will fight it out in court Thursday. The judge could order the FAS test.