NEW YORK (CNN/Money) - President Bush on Tuesday turned up the volume on his pitch for private accounts in Social Security in a panel discussion with ordinary Americans.

The president used the forum as another opportunity to reiterate his views on why he believes Social Security is in need of an overhaul.

Bush characterized as a crisis the eventual shortfall in the system -- when Social Security takes in less revenue than it must pay out -- which will be due in part to a declining number of workers supporting the pool of retirees receiving benefits.

By the time a worker in his mid-20s retires, the president said, "the system will be bankrupt. Think about a system that will be flat-bust."

Projections do indicate the system will only be able to pay a portion of the benefits promised under current law after 2042, according to the Social Security Trustees, or 2052, according to the Congressional Budget Office.

Nevertheless, the CBO estimates the system will be able to afford to pay retirees about 80 percent of promised benefits, which in real-dollar terms will still be higher than what today's retirees receive.

Critics of privatization proposals note that such projections should put to rest any notion that younger workers won't receive any money from Social Security when they retire.

The president also reiterated his position that any fix to the system should not include an increase in payroll taxes and should not affect the benefits of current and near retirees.

But he did not address other "fixes" that may be needed to resolve the system's solvency issues, fixes that are likely to cut future retirees' benefits.

Even proponents of privatization acknowledge that privatization doesn't take care of solvency in the long-term -- in fact, it is expected to create a near-term shortfall of up to $2 trillion in transition costs.

In recent days, those close to the president have hinted that he may consider changing the way starting benefits are calculated. That formula change is a key feature of the most widely discussed reform proposal, Plan 2, which was put forth by the President's Commission to Strengthen Social Security.

Bush asserted again that the investment choices available to workers in personal investment accounts would be safe.

"It's not risky," he said, comparing the choices in the accounts to those available to government workers in the federal Thrift Savings Plan, which is akin to a 401(k) for private sector employees.

The president has said workers would not be able to use their Social Security tax money to invest in individual securites, but rather would have a limited choice of "steady, reliable" funds that invest in stocks and bonds.

Critics have charged that no market-based investment can be described as "safe" because there is inherent risk assumed in exchange for the potential of higher rewards.