A Fairfax County police investigator service station owner was indicted yesterday on three counts of tax evasion by a federal grand jury in Alexandria.

The investigator, William A. Luzi of 2304 Locust Ridge Ct. in Falls Church, was charged in the indictment with understating his income by approximately $32,000 during 1972, 1973 and 1974.

U.S. Attorney William B. Cummings, who presented the case to the grand jury, said the charge stemmed from operation of the service station. Luzi and members of his family own Lee-Hi Shell at 5030 Lee Hwy. in Arlington.

If convicted, Luzi, a career officer due to retire from the force in three years, faces a maximum penalty of 15 years in prison and a $30,000 fine. Luzi could not be reached for comment.

Luzi is now on sick leave from his assignment in the checks and fraud division of the Fairfax County Police Department, according to a spokesman. Cummings said Luzi joined the Fairfax police force in 1962.

Luzi also served as a patrol officer in the Arlington Police Department in the 1960s, according to a staff supervisor there.

According to the indictment, Luzi reported taxable income of $8,770.07 for 1972 when he should have reported taxable income of $18,305.12. For 1973 he reported taxable income of $10,132.88 when the figure should have been $25,580.68, and 1974 taxable income of $18,937 when he should have reported $25,378.23, the indictment said.

Luzi allegedly owes the federal government $16,290.63 in back taxes, according to the indictment. Cummings said Luzi would have to pay that amount in addition to any fines imposed if he is convicted. Luzi is expected to be arraigned next Monday.