Katherine Jackson Case -- Judge Orders Investigator to Interview Children

The judge in the Katherine Jackson case needs help deciding to whom he should award permanent guardianship of MJ's children -- so he's ordered an independent investigator to interview the kids ... and report back asap.

According to court documents, obtained by TMZ, Judge Mitchell Beckloff has ordered a probate court investigator named Cary Ornelas to "prepare an investigation report addressing the status of the minor children and their currently suspended guardian, Katherine Jackson."

According to the court order, Ornelas has been authorized to interview the Jackson children at their school ... without notice.

Once completed, Ornelas' report will be submitted to the judge ... for his eyes only.

Michael Jackson's nephew TJ Jackson is currently the kids' temporary guardian, and he has already filed documents asking to make the guardianship permanent.

For her part -- Katherine says she has reached an agreement with TJ under which they will SPLIT guardianship of the kids.