Plunges in the stock market have taken a toll on the fortunes of the nation's pension funds for retired teachers and other public employees, with retirement systems nationwide reporting losses in the billions of dollars in recent weeks. The losses have worsened already-high unfunded obligations for plans that have promised more than $2 trillion in retirement benefits to public employees at a time of ballooning state and local government deficits. Experts stress that public employee pension plans are structured to be safe, long-term investments. But the unsettled economy has many teachers on edge--a point illustrated by fierce opposition to a plan by Georgia Gov. Sonny Perdue that teachers warn could threaten future cost-of-living adjustments, or COLAs. Under the Republican's proposal, the board of the Teachers Retirement System of Georgia could decide how much of an adjustment--if any--its 75,000 retirees get each year. That would end a rule put in place in 1969 giving an automatic 1.5 percent increase twice a year.