ST. PAUL, Minn. (AP) _ Attorney General Hubert H. Humphrey III took the stand today in a hearing to determine whether the Scott County prosecutor should be removed from office for her handling of alleged cases of child sex abuse.

Humphrey issued a report in February that was critical of the way Scott County authorities handled the investigation. His office took over the inquiry after county Attorney Kathleen Morris dropped sexual abuse charges against 21 adults.

He testified that he was frustrated when a federal-state investigation proved charges could not be refiled against the adults.

''I was presented, through the efforts of the people I had assigned to manage this matter, that there was no reasonable basis to proceed (with refiling charges),'' Humphrey told the three-member commission that will determine whether Ms. Morris should be ousted. ''There was a unanimous understanding there could be no process in these cases.''

On Thursday, Gehl Tucker, a former assistant Scott County attorney, testified that the charges were dropped last Oct. 15 because of concern for child witnesses.

Tucker said the effect of judicial rulings would have proved too trying for the young witnesses. One of the rulings gave defense attorneys the right to interview and conduct psychological exams with each child witness.

This ''had a tremendous impact on the children,'' Tucker said. ''They became very withdrawn. It was just highly traumatic for them.''

Of 24 adults charged with sexually abusing children, two were acquitted and one man pleaded guilty in a plea bargain.

After the remaining charges were dropped, a former defendant in the cases petitioned Gov. Rudy Perpich to remove Ms. Morris from office.

The petition alleges, among other things, that Ms. Morris lied when she said she dropped the charges to protect an investigation of ''great magnitude.'' That investigation turned out to be allegations by some of the alleged sexual abuse victims that other children had been murdered and mutilated at sex parties. State and federal investigators found no evidence to support those allegations.

A judge gave defense attorneys in the sexual abuse cases access to the notes from this investigation, which Tucker said was a factor in the decision to drop the charges.

Tucker said he talked with Ms. Morris about the impact of releasing the murder-mutilation notes, and he said it would have been impossible to continue the murder investigation if defense attorneys in the sexual abuse cases had access to authorities' reports on a daily basis.

''I don't think there was any way to maintain a viable investigation,'' Tucker said. ''I believed it (the murder-mutilation investigation) was of paramount importance.''

At the conclusion of the hearing, the commission, appointed by Perpich, is to recommend to the governor whether Ms. Morris should be removed as county attorney. The hearing resumed Aug. 1 after a seven-week delay and is expected to continue through next week.