Anticipating the demise of the Social Security system is like waiting for "the big one" to strike the San Andreas Fault - lots of people believe it's inevitable, but few are willing to change their lifestyle today to prepare for what might happen tomorrow.

Changes must be made to the nation's retirement system. That's been clear for years. And now the outline of likely alterations is coming into focus.The latest proposal - by the National Commission on Retirement Policy (NCRP), a panel of scholars, business people and politicians - focuses on "privatizing" the system by allowing at least part of the taxes you pay to go into an account that you control.

Over the next three weeks we'll look at how this plan will affect different generations of workers: pre-retirees, baby boomers and twenty-something Generation Xers.

Take Donald and Emily Roberts, for example. He's a 56-year-old draftsman for a construction company in Delmar, N.Y. ; she's a 55-year-old library assistant. Donald is a member of both the 401 and profit-sharing plans at work and Emily contributes 3 percent of her salary to a retirement plan.

Under the NCRP plan, the Robertses may begin to collect full Social Security benefits at age 66. In fact, the NCRP plan wouldn't change much about the couple's expectations from Social Security.

But it would put a dent in Emily's expected benefit. Like many women of her generation, Emily has a shorter work history and lower income than her husband. So her retirement benefits will be based on Donald's earnings.

Under current law, Donald would be entitled to a monthly benefit of about $1,235 and Emily would receive a benefit half that size, for a combined monthly benefit of $1,853.

But under the NCRP proposal, spousal benefits gradually would be reduced to one-third - rather than one-half - of the higher-earning spouse's. By the time the Robertses retire, Emily's Social Security benefit will be only about 41 percent of Donald's amount, shrinking the couple's retirement income by $111 per month from what they'd get under the current system.

And they wouldn't have a government-mandated personal savings account to offset that loss because that part of the plan only applies to workers age 55 and younger at the time of enactment.