A trial lawyer waging his second campaign for the Democratic nomination for Montgomery County prosecutor yesterday accused the three-term incumbent, Andrew L. Sonner, of insensitivity and "a callous neglect for victims' rights."

Daniel J. Cassidy, who lost to State's Attorney Sonner in 1978 after an unusually bitter primary battle, called Sonner soft on criminals. He pledged that if he is elected he would institute a policy of bringing victims to court to testify at the time a defendant is sentenced.

Assistant State's Attorney Michael Mason, responding for Sonner, called the allegation about insensitivity to victims "inaccurate and totally without merit. A large portion of the resources of this office are dedicated to victim and witness assistance."

Cassidy made his accusations at a noon press conference, flanked by the mother of a 1976 murder victim and the mother of a teenager killed when he was hit by a car. Both women were dressed in black and wore blue and white Cassidy buttons.

Doris Michaud's 22-year-old son Daniel was slain in the parking lot of a Bethesda Holiday Inn and robbed of a bag of change.A man arrested for allegedly trying to cash in the change at a bank was indicted on a first-degree murder charge, but Sonner's office later dropped all charges for lack of evidence.

Mrs. Michaud said, "This man is free. He will never be brought to trial and that is due to the state's attorney." She said Sonner has not returned her phone calls.

A spokesman in the state's attorney's office said the charges were dropped because the defendant had an alibi supported by a witness who passed a lie detector test. The spokesman said Mrs. Michaud was informed that charges were being dropped.

The second mother, Carol Weiger, said her 16-year-old son was killed while walking down Rte. 28 in Gaithersburg in 1977. A motorist arrested 15 minutes later near the scene was charged with driving while intoxicated, hit and run, and auto manslaughter. The manslaughter charge was dropped and the drunk driving charged reduced to driving while impaired. The driver received two $300 fines and lost his license.

The spokesman in the prosecutor's office said the charges were reduced because there was insufficient evidence to prove manslaughter, since the young man who was killed had been walking down the middle of the road and even a sober driver had to swerve to avoid hitting him.

The spokesman said the prosecutor's office has five full-time victim-witness coordinators, and, while victims are not routinely brought into court during sentencing, they are kept informed of trial dates."In every case, we make an honest effort to impress upon the court the impact of the crime on the victim," he said.