Proponents of mandatory Social Security coverage for federal and postal workers argue that bringing feds into the fold would eliminate what they call windfall Social Security benefits for civil servants.

Under the Civil Service Retirement System employes pay 7 percent of their gross salary into the fund. They get back retirement benefits (which are taxable) based on income and length of service. Like most other staff retirement plans the more they make and the longer they work, the more they get in pension.

Social Security is different. Its benefits (tax-free, but generally much lower than civil service benefits) are structured so that persons who pay the maximum into the fund for the maximum time get back benefits that are proportionately smaller than persons with low income or who pay into the system only a relatively short time.

Under Social Security, for example, a person who earned minimum wage for his entire working career and made minimum contributions to the system would, at age 65, get benefits equal to almost 58 percent of his preretirement income. The person who earned more, and paid the maximum into Social Security, would get back only 25 percent of preretirement income.

Because there are different retirement ages to qualify for full benefits under the two programs (55 for feds vs. 65 under Social Security), many civil servants work under Social Security-covered jobs for a relatively short time to establish eligibility that gives them what many consider windfall Social Security benefits plus federal annuities.

That feature is one reason the national commission studying ways to improve the financial health of Social Security wants to bring feds into it, and force them to contribute to the system for their full careers in or out of government.