PITY THE CITY property taxpayers. They have just been handed a grievous insult to add to their recent injury was the latest 42 per cent average increase in real estate assessments on single family properties. The insult: A survey of the 20 most valuable commercial properties in the city shows an actual decrease in tax liability over the last four years. Indeed, during that period the assessed value of all residential property increased by 66 per cent - while the assessed value of all business properties increased by only 23 per cent. The specific details of the survey, which was prepared by Carl Bergman of the city auditor's office, are equally intriguing - and no less so to us by reason of his newspaper's particular financial interest in the matter.

Since 1974, assessments on seven out of the top 20 commercisal properties - The Washington Post building, the Sheraton Park, the Towers (4201 Cathedral Ave. NW), 1025 Connecticut Ave., 400 Massachusetts Ave. NW, the Mayflower and the National Press Building - have actually declined. on another property, the Capital Hilton (formerly Statler), the assessment has remained constant. "It is quite apparent," the report states," . . . that several of the major commercial properties of the District have been given a free ride over the last several years."

Whether the taxes that did get paid on these properties amount to a "free ride" is detable, to say the least. Still, the disparities between commercial and residential assessments are puzzling, and the explanation offered by mayor Washington and other officials are not much help. Donald Beach, chief of the city's real estate property assessment tax admonistration, has observed that as a general rule residential assessment have leaped ahead of commercial assessmnets because in-town living has become increasingly popular, accelerating the turnover of homes, while commercial development continues to lag. He also denies that there is any specific government policy to give business a special tax break.

The assessed value of office buildings and hotel is determined primarily by the amount of rent collected or the income produced from the building. When rent controls hold down the rents , the values also get down, Mr. Beach said. Then, too, there's depreciation that must be taken into acount; those buildings somehow age far more dramatically than most of the homes that the city has been scrutinizing with such painful intensity. It is also argued that, over a long cycle, older commercial buildings are razed and replaced by new ones, and that property assessments respond accordingly. maybe so.But city homeowners have every reason to question any assessment procedures that produce an erratic pattern. For example, the Towers shows a 7 per cent decrease in the fiscal 1974-78 period. Yet homeowners only blocks away were hit with increase of more than 75 per cent in that same period. In 1974, according to Mr. Bergman, single-family homes and commercial properties each accounted for 39 per cent of the city's tax base. By this year, single-familly homes accounted for 49 per cent - nearly half - while commercial property slipped to 36 per cent.

Some city council members are already supporting programs to give homeowners soma tax relief. And Mayor Washington is scrambling to get out in front on this issue. After proposing a one-time-only reduction, he's now drawn up a convoluted scheme that ties property taxes to age and ability to pay, turning it into a sort of second income tax. The council, acutely aware of the local administration's casual tax procedures over the years, should oconcentrate on making the commercial and residential tax burdens more equitable - not on enacting another program that would invite still more maladministration by city hall.