In need of straight answers from city government? Take a look at "Indices," a statistical index just published by the District Office of Policy.

The 253-page book includes multifarious municipal minutiae: tax facts, service breakdowns, court gestures and figures on metropolitan life, death, imprisonment, utilities and insurance for 1986.

The District's 627,400 residents, living on its 60 square miles of land and nine of water, earned $11.9 billion. That translates to a per capita income of $18,980, which is 31 percent higher than the national average.

Though 56 percent of the District is exempt from real property tax, the rest brought in $437.3 million in taxes, or about 11 times the profits made by the lottery. The District owns 1,655 acres, assessed at $1.7 billion; except for educational use, the largest category is vacant land.

On 1,102 miles of streets, 285,600 registered motor vehicles ran under 66,483 street lights and past 13,590 parking meters (which collected an average of $695 each during the year). On the darker side: 6,105 car thefts were reported, resulting in the arrest of 1,480 adults and 1,015 juveniles.

Public schools enrolled 86,893 children, and private schools, 14,773. Disparate institutions of higher study (including DeSales School of Theology, Defense Intelligence College and the Corcoran School of Art) taught 46,066 undergraduate and 31,605 graduate students.

The Blue Plains Wastewater Treatment plant in Southwest processed 293.4 million gallons of wastewater -- and generated 1,804 tons of sludge -- each day.

Teachers, students, demographers, city planners, taxpayers and trivia fans -- all can obtain "Indices" from the Office of Policy in Room 208 of the District Building, 1350 Pennsylvania Ave. NW. The cost is $5 for District residents or nonprofit institutions and $15 for businesses. In addition, copies are available at public libraries and the offices of advisory neighborhood commissions. For information, call 727-2585.