Don't make the mistake of assuming that the members of the underground economy are all shady, sneaky people of the sort you never see. They're much more likely to be your neighbors.

The General Accounting Office did a study earlier this year of people who, though they have taxable incomes, never even file returns, as opposed to those who do file but do not report all income.

The agency found that these non-filers are by no means limited to waiters who don't report tips or carpenters doing a little extra work on the side.

The reports noted, for example, that:

Six percent of all professional and technical people fail to file income tax returns.

Five percent of all managers and administrators fail to report their income.

Thirteen percent of all service workers do not declare their income.

Twenty-two percent of all tax dodgers have attended or were graduated from college. (Meanwhile, 31 percent of all non-tax-cheats attended or were graduated from college.)

Southerners are by far the worst offenders. More than 11 percent of all southerners do not bother to file income taxes, making up nearly 40 percent of all tax cheats in the country.

Another abnormally large group of tax cheats is the elderly. Twenty-one percent of all people over 70 do not file their returns, while only 8 percent of those from the 30-to 49-year-old age group fail to file.

The Treasury Department reports separately that an estimated $1 billion -- half of the GAO's estimate of the total government loss due to tax evasion -- is lost because salesmen and other so-called "independent contractors" fail to file returns.

The category of "independent contractors" includes such traditional business people as real estate agents, truckers, poll takers, cab drivers who own their own cabs, street vendors and others.

The GAO study indicates that, by and large, professional people, managers and administrators are more trustworthy when it comes to filing tax returns than service workers, laborers and clerical workers.

In some occupations, GAO reported, more people failed to file returns than filed them.

For example, nearly 65 percent of all private household workers did not file tax returns, the GAO said.

About half of all non-agricultural laborers also failed to report their incomes, the study said.

A third of all farm laborers were non-filers.

While 8 percent of all home or apartment dwellers failed to report their income, nearly 40 percent of all rooming house residents and 30 percent of all hotel residents were found to be tax cheats, the GAO said.