TRENTON - William Liberty began as a trash collector in Lindenwold, Camden County, 37 years ago and worked his way up to public works supervisor. Until recently, he figured he would hold on to the job until he turned 65.

But last week, at 62, he was preparing his retirement papers, joining a rush among New Jersey public employees.

Liberty's reason for getting out now: He is feeling the sting of a campaign by Republican Gov. Christie and a growing number of other public officials across the country to balance their budgets by making government employment - and retirement - less lucrative.

Liberty's pay has been frozen for two years, he has been told to take unpaid furlough days, and now, "it's going to get worse," he said. Pension proposals announced this week could reduce how much he receives when he retires.

Since 2008, at least 20 states - including New Jersey, Rhode Island, and Wyoming - have rolled back pension benefits or seriously considered doing so. That is not only for new hires, but also for current employees and retirees.

It's not just a U.S. phenomenon. In France on Wednesday, lawmakers voted to raise the retirement age to 62 from 60. France would become the latest European Union country to require workers to stay on the job longer because of a deficit-plagued pension system.

To be sure, the looming benefit changes in New Jersey, proposed by Christie on Tuesday, are not the only reason many public employees in the state are retiring. Some say they want to spend time with their grandchildren or go fishing, for example. Others complain that government layoffs and other cutbacks are making work unbearable.

But some employees figure that by retiring now, they can lock in certain benefits before it is too late.

Christie has warned that New Jersey's pension fund will go belly up unless something is done to close the $46 billion gap between how much the state expects to bring into the system and how much it has promised to workers. Other states' pension funds are in shaky condition, too.

The Pew Center on the States reported this year that, as of 2008, state and local governments had pension obligations totaling $3.35 trillion - $1 trillion of that not covered by the future stream of government and employee contributions specified under current law.

Only four states - Florida, New York, Washington, and Wisconsin - had fully funded pension systems as of 2008, the report said.

Part of the reason for the gap is that in tough times, states often skip paying their share into retirement funds. New Jersey, for instance, is skipping its $3.1 billion in payments this year.

The problem is compounded when investments lose money, as many have in recent years. In 2008, for instance, the Pennsylvania State Employees' Retirement System fund had investment losses of nearly 29 percent.

Among recent developments:

Mississippi's state and local government workers now must put 9 percent of their pay into the state retirement system, up from 7.25 percent.

In 2009, Rhode Island reduced cost-of-living increases and tightened eligibility requirements for retirement.

In Wyoming, as of Sept. 1, employees will have to start paying 1.4 percent of their salaries into a pension fund - the first time in a decade the workers have had to contribute anything.

Vermont this year changed the retirement age for many current employees. They must be 65, or their age and years of service must add up to 90. Previously, retirees had to be 62, or have 30 years of service, regardless of age.

Lawmakers in Colorado, South Dakota, and Minnesota rolled back cost-of-living increases this year for retired public employees.