Gov. Blagojevich's administration today is expected to seek an investigation into miscalculations that caused a generous early retirement program for state workers to unexpectedly quadruple in cost, leaving taxpayers holding a $2.45 billion bill.

The program -- engineered by Gov. George Ryan and passed by the Legislature in 2002 -- enabled 11,000 state workers to retire early. In some instances, retirees as young as 50 were allowed to start drawing pensions worth up to 80 percent of their salaries -- income that carried the added benefit of not being taxed by the state.

Ryan's office initially projected the cost of the program at $622 million over 10 years. But various sweeteners and a greater-than-expected turnout of wannabe retirees caused the program's price tag in the coming decade to balloon to an estimated $2.45 billion.

Blagojevich's budget chief, John Filan, is expected to ask Comptroller Dan Hynes to undertake a probe into why cost estimates were so grossly askew, particularly after lawmakers approved the plan thinking it eventually would pay for itself by inducing high-paid employees off the payroll and not having their positions filled.

Blagojevich's budget team originally planned on booking $70 million in the fiscal 2005 budget to pay for the retirement program, but that commitment could jump to as high as $380 million -- though that is somewhat of a moving target.

''The point here is because this is such a tremendous fiscal impact on the state, there needs to be an independent set of eyes and ears investigating what went on behind the scenes, what was said in public, what was disclosed and what wasn't disclosed,'' said one state government source familiar with the administration's intentions.

''Because this has turned out to be one of the worst financial scandals in state government, this cries for some kind of an investigation to determine how this happened so that it never happens again,'' the source said.

If a probe is launched, there is no hope of retrieving any of the funds by reversing the retirement program. The state's Constitution protects public employee pensions from being diminished.