Do U.S. workers abuse sick leave before retirement, or does the pre-retirement jump in sick days mean they are sick? On Jan. 26 this column reported on a congressional study that showed a 10-fold jump in sick leave use before retirement at the General Services Administration.

That report triggered lots of mail, all of it from people who question the report and the conclusions that many will draw from it. This is what people are saying:In response to the column on "The Pre-Retirement Sick Leave Syndrome" . . . I would like to commend you . . . for pointing out . . . that the General Accounting Office study is just the kind of report that . . . politicians love to use to bash federal workers.

You were also correct to point out that GAO did not release any statistics to support their charges. There is one additional point that you did not make . . . and it is a point that . . . seriously cripples the GAO thesis, namely that lazy, shiftless feds are abusing the sick leave program by using up all their leave right before retirement.

The GAO thesis is based on the idea that the direction of causality runs from (1) retirement is approaching; therefore, (2) use up all sick leave. It is also quite possible that the direction of causality runs in the opposite direction, namely that (1) debilitating or fatal illnesses result in the use of all sick leave until the worker is no longer able to stay on the job and then (2) the worker is forced to retire.

In 15 years of federal employment I knew only one employee who fell into the former category . . . and several who fell ill . . . used up their leave and were forced by illness to retire. Most employees, fortunately, fall into neither category. They do their jobs, using leave only when necessary, and accumulate leave to apply it to their longevity.

In statistical analysis, one of the most difficult things to establish is causality (some claim it is impossible). It's apparent . . . that GAO took some data and used it to put federal workers in the most unfavorable light possible when, by presenting it in a different manner, they could have given workers . . . the credit they deserve. J.J., Annandale

GAO's report . . . gives the impression that heavy sick leave use prior to retirement is plain and simply an abuse. But consider this: For many years medical statistics seemed to indicate that men in full retirement could expect to live only 3 years. Now, it turns out many of those men were sick when they retired, and when these cases are factored out, there is no shortening of life due to full retirement for healthy people. What this suggests . . . is that many people must be retiring because they have a serious illness . . . and are not just after some time off at full pay before they retire.

Consider also that when a person has met . . . service requirements, there may still be a wide spread in years for optional retirement -- from as early as age 55 to age 75 or whatever. Why do people decide to retire at a specific age? Could it be their knowledge of impending or actual illness? Could it be that they aren't all just a bunch of cheats? T.M.C., Bethesda