Attorneys for Terrence G. Johnson, the 16-year-old youth convicted in the slaying of a Prince George's County police officer, argued today the conviction should be overturned because Johnson should not have been tried as an adult.

Johnson, a black youth serving a 25-year sentence for manslaughter and a handgun offense in the shooting of one white officer, was acquitted on grounds of temporary insanity of slaying a second. His jury trial last March in the shooting deaths of the two officers exacerbated racial tensions in the county.

R. Kenneth Mundy, one of his attorneys, maintains that "the offenses as alleged do not evidence any prior planning or preparation, and at worst were spontaneous acts which one would associate with a response of immaturity." That argument was contained in legal briefs submitted to accompany today's arguments before the Maryland Special Court of Appeals.

If tried and convicted as a juvenile, Johnson could only be incarcerated until his 21st birthday. His request to be tried in Juvenile Court last year was denied by Prince George's Circuit Court Judge Vincent J. Femia.

The slayings of officers Albert M. Claggett IV and James B. Swart occurred at the Hyattsville police station in June 1978 as Johnson and his older brother were being questioned in connection with the burglary of a laundry coin box.

Johnson was convicted in Claggett's death but acquitted of Swart's; the jury also acquitted him of first-degree (premeditated) murder charges.

At his trial, Johnson's lawyers argued he shot Claggett because he feared for his life and then shot Swart in an attempt to escape.

Yesterday his lawyers argued that Circuit Judge Jacob S. Levin, who presided at the trial, erred in his instructions to the jury by failing to give them the option of convicting Johnson of involuntary manslaughter -- a lesser charge in Claggett's death.

Assistant Attorney General Stephen B. Caplis argued that the evidence "would be inconsistent with involuntary manslaughter" but was sufficient to convict Johnson on other charges. He said that if the verdict were overturned on any basis other than insufficient evidence, the state could reinstate any of the charges against Johnson except for those of which he was acquitted.