Circuit Judge Cypert O. Whitfill declared a mistrial last night after a jury of seven men and five women was unable to reach a verdict in the first-degree murder trial of a former Edgewood man accused of fatally shooting his wife.

Harry Phillip Gross III, 45, of the first block of S. Ellwood Ave., Baltimore, was charged with fatally shooting his wife, Clara Jean Gross, 43, in their mobile home on March 7, 1993.

Prosecutor Joseph I. Cassilly, the Harford County state's attorney, contended that Mr. Gross wanted to collect on a $50,000 life insurance policy after learning his wife intended to leave him and change her beneficiary.

David Henninger, attorney for the defendant, argued that the .38-caliber pistol discharged when his client grabbed it to prevent Mrs. Gross from shooting herself.