PHOENIX — A judge has rebuffed a constitutional challenge to an Arizona law that allows the directors of state agencies to disregard the conclusions of independent hearing officers.

In a 26-page ruling, Maricopa County Superior Court Judge Douglas Gerlach rejected claims that Greg McKay, then the director of the Department of Child Safety, acted improperly when he concluded that Phillip B. — the only identity provided in court records — was guilty of child abuse for rough handling of a youngster. The charge is that the caregiver was accused of placing his forearm against the neck of a 13-year-old boy to the point where the child’s face turned red and he was unable to breathe.

That resulted in the caregiver not only losing his job at a group home for boys but having his name entered into the Arizona Central Registry as a child abuser for the next 25 years.

The problem, said attorney Adi Dynar or the New Civil Liberties Alliance, is McKay’s conclusions were directly contradicted by the findings of the administrative law judge who heard the evidence and exonerated Mr. B.

Dynar contends that it is improper to let McKay — or, for that matter, the head of any state agency — substitute his or her judgment and conclusions about the fact for those of the hearing officer who actually conducted the hearing and listened to the witnesses. Dynar asked that the law allowing that be struck down as unconstitutional.

Dynar called it a “stacked process.’’

“The only independent fact finder in the administrative process employed here was the administrative law judge,’’ he wrote in filing the suit. “The ALJ heard testimony, made credibility determinations, and entered finds of fact and conclusions of law into the record.’’

But under the way Arizona law works, any appeal from the ALJ’s decision — whether by the person who was the subject of the complaint or the agency that filed the complaint — goes back to the head of the agency, “the very same agency that investigated the prosecuted the charge against Mr. B. in the first place.’’

“Under this procedure, DCS and Director McKay not only investigated and prosecuted the child-abuse charge against Mr. B., but also acted as the ultimate fact finder and judge,’’ Dynar wrote. He asked Gerlach to invalidate the law that allows that process to happen.

The judge didn’t see it that way. He called it “well-settled law’’ that the combining of investigatory and adjudicatory functions in a single agency does not violate due process absent a showing of actual bias.

“And what the Phillip briefs attempt to pass of as bias is merely self-interested speculation, suspicion, apprehension or imagination, which is not enough,’’ the judge wrote.

Gerlach rejected arguments that the system results in an unconstitutional concentration of power in the director of the department.

He said there is no evidence that McKay participated in the initial investigation nor prosecuted the case. Gerlach said McKay reviewed the record before reaching his own conclusions.

Dynar promised an appeal, saying in a prepared statement that the judge did a “double-dodge.’’

“The court decided not to review the myriad due-process and separation-of-powers problems for factual reasons, ‘’ he said. “At the same time, the court decided not to take a look at the facts to avoid the serious legal problems with Arizona’s administrative law.’’