Three weeks after pleading guilty of two misdemeanor counts of filing false tax returns, a Fairfax County police detective was granted a full disability retirement by a retirement board that was unaware of the detective's court plea.

The board's decision enables detective William A. Luzi to begin drawing an annual pension of about $14,520, two-thirds of his police salary, a county spokesman said yesterday. Had Luzi been convicted of the felony tax charges that he originally faced, he could have lost all his pension benefits.

Police investigator William A. Luzi, who yesterday was fined $500 and ordered to perform 200 hours of community service by a federal judge in Richmond, had been "ambiguous" about his legal problems when he testified before the county's police retirement board on June 12, a board member said.

"As far as I recall he didn't testify to pleading guilty," said Edwin A. Williams, one of three board members who granted Luzi a disability retirement at two-thirds of his police salary.

"He said the situation (regarding the tax charges) was kind of up in the air," Williams said.

The retirement board found Luzi, 42, who had been assigned to the checks and fraud division, fully disabled on the basis of a doctor's testimony which concluded that the detective suffered from "hypertension with an anxiety reaction."

That testimony, by Luzi's private physician, Dr. David J. Kiernan, was challenged by another physician who examined Luzi for the board. Dr. Nicholas Cirillo told the board that Luzi "suffered from severe situational anxiety reaction during which time (his) blood pressure is occasionally elevated." But the physician said Luzi could perform administrative duties "without difficulties."

Board member Williams said he and the two other board members -- Fairfax police officers Ed Bohn and Tom Croup -- found Luzi "unable to do his job as a police officer" and granted him a disability retirement.

Luzi, who has served 17 years with the police department, was earning about $22,000 when he retired. a police spokesman said.

Luzi could not reached for comment yesterday. Bohn and Croup were also unavailable for comment.

Luzi pleaded guilty in Alexandria May 24 to two misdemeanor charges of submitting false documents to the Interanl Revenue Service. When he made the pleas, three felony counts of income tax evasion against him were dropped.

Fairfax police spokesman Warren Carmichael said yesterday that Luzi had filed for the disability retirement before he was indicted April 2 on the tax charges.

Carmichael said, that under county regulations, once an officer files for disability retirement the policce department is excluded from the decision to grant retirement benefits.

"This decision was made by the retirement board. This is not the police department's fault. This is the system," Carmichael said.

The retirement board is made up of two members elected by police officers, two members appointed by the Fairfax Board of Supervisors and the county director of financce. Two members were absent from the hearing when Luzi was granted his retirement.

In Richmond yesterday, District Judge Robert R. Merhige suspended a one-year jail term for Luzi and placed him on probation for two years. Merhige ordered Luzi to complete the 200 hours of community service within those two years.

According to Brain Gettings, a lawyer who represented Luzi in May, the retired policeman's guilty plea meant that Luzi "misinformed the IRS as to the source" of $3,000 in income. Luzi and his family operate a service station on Lee Highway in Arlington. Income from the station was the focus of the governments case, Gettings said.

According to the IRS, Luzi presented false documents to an IRS agent in an attempt to avoid paying taxes on $5,186.86 of income earned in 1972 and 1973.