WASHINGTON -- The House Republican plan to overhaul Social Security requires retirees to give up their guaranteed benefit level if they want a personal account that can be passed on to heirs, GOP aides said Monday.

Only those who invest the accounts in government securities while they are working and in an annuity when they retire can be certain of receiving the full Social Security benefit they are promised, the aides said.

Other investment decisions would expose individuals to the ups and downs of the financial markets. That means their monthly benefit could wind up lower or higher than now envisioned. The aides, who work for the House Ways and Means Committee, described details of the bill to reporters on condition of anonymity.

Creation of personal accounts that give workers a nest egg they can pass along to their heirs has been a major selling point in the GOP drive to overhaul Social Security.

Personal accounts would be established for all workers except those who decline one under the legislation introduced last week.

The program envisions individuals receiving a monthly benefit that consists of a blend of traditional Social Security -- from the program's trust funds -- and money from personal accounts.

Aides also disclosed that in many cases, a personal account that is inherited by a spouse would be used to pay a portion of the survivor benefit they are entitled to.

The effect over time would be to reduce the amount of money in the inherited account while easing the burden on the Social Security trust funds.

If surviving spouses lack an account of their own, they can decline the inheritance and receive the benefit that current law provides, according to the aides.

The legislation was formally filed in the House last week, although no vote is expected before September at the earliest.

It marks an attempt by House Republicans to meet President Bush's call for changes in Social Security while minimizing political risk at the hands of Democrats who accuse them of seeking to privatize the program.

As such, it is sharply scaled back from Bush's proposal, and an administration spokesman spoke carefully about it during the day.

"The president is committed to two elements. One is improving, restoring the solvency of the Social Security system and the second is creating personal retirement accounts for individuals," said Ben Bernanke, chairman of the president's Council of Economic Advisers. "... We want to see both of those."

Unlike Bush's proposal, the House GOP measure uses surplus payroll tax funds to establish personal accounts rather than allow each worker to divert a portion of their payroll taxes.

Another key difference is the bill does not mandate a reduction in guaranteed benefits for any future retirees, although officials have said steps to increase the solvency of the program may be added at a later date.

The measure has only a modest impact on the projected solvency of Social Security.

Aides said that under the terms of the bill, Social Security trust funds would begin paying out more than they take in beginning in 2017, the same as current forecasts. The trust funds would become depleted in 2043 under the bill, they said, citing an official estimate from the program's chief actuary. That represents a two-year improvement from the current forecast.

The bill would make a major change in the Depression-era program, however, by taking money from the trust funds and distributing them into personal accounts set up in the name of individual workers. The distributions would stop when the trust fund surplus is exhausted, in about a decade, but the accounts would remain in place.