WASHINGTON -- President Bush believes Americans are so eager to join the "ownership society" that, given a chance, two-thirds of those eligible would divert funds from Social Security into the personal investment accounts he proposes.

But when public employees in seven states were offered the opportunity for similar accounts during the last decade, nowhere near two-thirds signed up for them. In many instances, the figure was closer to 5%.

Bush has argued in campaign-style events from Fargo, N.D., to Blue Bell, Pa., that Social Security account holders could make more money for retirement on their own than they can count on from the New Deal-era fixed-benefit program.

But when Nebraska's state and county workers were given do-it-yourself accounts, they made so many investment errors that they ended up making less than colleagues with fixed-benefit pensions -- and less than what analysts have said is needed for old age. Their poor performance led the Nebraska Legislature two years ago to junk the accounts for new employees.

While Americans are just beginning to grapple with the president's proposal for private accounts, employees and retirement officials in Michigan, Montana, Washington, West Virginia and other states have discovered that the accounts can fall far short of their promise. Their experiences sound a cautionary note for Bush as well as for California Gov. Arnold Schwarzenegger, who has proposed switching public employees to private accounts starting in 2007.

The accounts Bush is proposing are not a precise match to the ones states have offered in recent years. And the low signup rate for accounts among state workers may be partly because more of them are covered by generous pensions than are American workers generally, so they may feel less need for the accounts. But the tepid response to accounts in some places casts doubt on one of the central premises of the Bush plan: that Americans are clamoring to join the investor class.

The poor performance of many of the accounts leaves experts to wonder whether most people, even among those who want to make their own retirement investments, have the time or knowledge to do so successfully.

"If people have private accounts in Social Security and they're left to make the decisions themselves, the results likely will not be positive," said Anna Sullivan, executive director of the Nebraska Public Employees Retirement Systems, which replaced its private account system with a centrally managed plan in 2003.

Joseph Jankowski, executive director of the West Virginia Consolidated Public Retirement Board, said: "The vast majority of people don't have the inclination or comfort level to be responsible for their own retirements." West Virginia board officials are debating whether to drop the state's private account plan as Nebraska did.

The president's plan assumes that two-thirds of working Americans under 55 -- an estimated 90 million people -- would quickly choose to take a substantial chunk of the payroll tax money that now goes to Social Security and shift it into private investment accounts beginning in 2009. (Those 55 and older would not be eligible for the accounts.)

But of more than 1.5 million public employees offered the choice of accounts at various points in the last decade, about 125,000, or 8%, have signed up. The lion's share of those were during the stock market boom of the late 1990s. The sign-up rate in many of the states has been about 5%.

White House aides said the two-thirds estimate was based on a 2001 Social Security Administration analysis of an account arrangement similar to, if somewhat more generous than, Bush's current proposal. But they said they saw no problems if the accounts were to draw a lower sign-up rate.

"The president has made it very clear these accounts would be strictly voluntary," said deputy White House spokesman Trent Duffy. "If an individual wants to pursue the benefits that we believe are present ... that's fine," but the White House plan doesn't require high participation.

The White House argues that Social Security will probably require painful cutbacks to avert financial ruin. And it hopes private accounts would help ease the pain when benefits from the traditional part of the system are reduced.

"The personal accounts are the only thing that makes this whole effort worth doing," said Grover Norquist, a leading proponent of private accounts, who is president of the advocacy group Americans for Tax Reform.

Social Security and traditional pensions are "defined benefit" systems, meaning that the worker is entitled to a predetermined level of benefits; the employer or the government -- not the individual -- manages the money, bears the economic risks and makes sure people get certain, fixed benefits in retirement.

By contrast, the accounts that Bush and Schwarzenegger are proposing would be "defined contribution" arrangements similar to today's 401(k) plans. In these plans, the employer's responsibility ends with a fixed contribution to a worker's account. From there on, it is largely up to individuals to bear the risks and reap whatever rewards result by the time they retire.

Among the states, by far the biggest test of private accounts' popularity in recent years has come in Florida, where Gov. Jeb Bush, the president's brother, proposed replacing public employees' defined benefit pensions with a mandatory defined contribution plan.

Although the governor eventually compromised on a voluntary plan, state officials still predicted a stampede. Early surveys of Florida's 600,000-plus public employees suggested that more than half would go for accounts. But since the accounts' introduction in 2002, 43,000 employees, or about 7%, have enrolled.