Daveigh Chase's father wants a judge to deny her mother's request to be appointed as the administrator of her 6-figure estate ... TMZ has learned.

According to new legal docs, obtained by TMZ, John Schwallier opposes Cathy Chase's motion to be appointed the administrator of the 'Ring' star's estate.

Instead, the docs say Schwallier nominated a woman named Megan Boling -- who describes herself as a neutral licensed professional fiduciary -- to object to Cathy's petition and take on the job instead. If that's denied, the docs request the appointment of a public administrator.

The docs note Daveigh was emancipated from Cathy as a minor due to "allegations of financial irregularities" by Cathy ... and they were "separated" ever since.

The filing says Daveigh was actually "estranged" from both parents at the time of her death, which is why a neutral administrator should be in charge.

As TMZ previously reported, Cathy asked to be in charge of Daveigh's estate, reasoning she was never married and had no children.

Daveigh was living in an RV on Los Angeles's Skid Row when she died in June.

Her cause of death was determined to be acquired immunodeficiency syndrome (AIDS) and drug use ... and was ruled to be natural.