According to court docs obtained by TMZ ... prosecutors want Judge Michael Pastor to bar Steve Robel -- a key Santa Barbara County Sheriff's investigator in the 2005 MJ molestation trial -- from testifying in Murray's defense. Robel is on the defense witness list.

In fact, prosecutors want all references to alleged molestation barred from Murray's trial, on grounds it has nothing to do with MJ's death and would merely inflame the jury.

And, prosecutors have also asked the judge to block the testimony of a number of doctors who treated Michael Jackson but were not involved in caring for MJ on the day of his death. This is a huge motion that could have a profound impact on the case. As TMZ first reported, the defense will argue that dozens of doctors had addicted MJ to prescription meds -- including Propofol -- and they are largely responsible for the condition Michael was in the day he died.