Maine’s leaders are working on a plan to help meet the state’s long-range obligation to fund its public employees’ retirement needs.

But their idea isn’t new — in fact, it’s the better part of a century old.

It would shift some of the state’s obligation to Social Security, the federal system implemented in 1935 that now covers most public and private workers nationwide.

But 6 million U.S. public employees work outside the Social Security system, a policy that a few states, including Maine and Louisiana, are reconsidering.

Workers, however, may remember reading that Social Security is having to cash in some of its Treasury bonds, years ahead of schedule, to pay current benefits.

While that is a direct result of the current recession and may cease once the economy recovers, sooner or later income from the bonds (which must be paid from general federal revenues) will resume as a full-time practice.

That has increased the volume of calls to put the system on a sounder footing by altering Social Security benefits, increasing the amount of total income subject to payroll taxes or raising the retirement age.

Thus, joining it may not seem like the best guarantee public employees could receive to fulfill the pension-fund promises they have received from the state.

But the fact that the state’s pension fund lost $2.25 billion in 2008, according to a story Wednesday in The New York Times, provides the pressure that leaders, including both Democrats and Republicans, are experiencing to diversify the funding sources that undergird their obligation to provide workers with the full amount of their promised retirement income.

Maine is one of a handful of states that do not require most of their employees to participate in the federal retirement plan that covers nearly all private workers.

Government entities can participate or not, as their leaders see fit. In most states, even where most state workers are covered by Social Security, teachers, police and firefighters are still excluded because their retirement criteria don’t often conform to the federal age and work-credit standards laid out in the Social Security statutes.

Maine is in a better financial position than states like California and Illinois, which shortchanged their retirement plans for decades.

The Pine Tree State has a constitutional requirement to make its full contributions, with catch-up payments also required to cover the period before the provisions took effect in 1997.

But that hasn’t stopped the fund from suffering losses due to the recession, as previously noted.

The reason Maine’s participation in Social Security (after a phase-in period) is being considered now is partly to protect the state from having to fund huge catch-up payments in case investment returns suffer a precipitous decline due to even worse performance by the national economy.

The Times said the principal reason the state has met its obligations to date is because only one in five state employees works long enough to draw a pension. If the state were paying full benefits to all current or past employees, it would have exhausted its retirement funds long ago.

For private workers used to counting Social Security benefits as a reliable part of their retirement planning, the question may be why the state has waited so long to consider joining a system that requires no commitment to maintain a fund of its own.

The state’s obligation would be to pay the employer’s share of benefit contributions, currently 6.2 percent of salary, with contributions capped once pay reaches $106,800 (in 2010 — the figure may rise in later years depending on cost-of-living increases or changes in the law).

Employees would contribute identical amounts. And they would end up with a sizeable part of their pension coming from a portable, federally supported system that they would likely continue to participate in even if they left the state’s work force before retirement age.

To many state lawmakers and officials, that’s a better deal than workers get now.

Of course, it remains to be seen if the workers will agree. Maine is in a better financial position than states like California and Illinois, which shortchanged their retirement plans for decades. The Pine Tree State has a constitutional requirement to make its full contributions, with catch-up payments also required to cover the period before the provisions took effect in 1997. But that hasn’t stopped the fund from suffering losses due to the recession.