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President Bush on Thursday flatly ruled out raising payroll taxes (search) to ensure the solvency of Social Security (search) as he opened a push for historic changes in the retirement program.

Bush renewed his call for legislation that would let workers create private retirement accounts (search) within the government-run program.

He sidestepped questions about whether the nation can afford to borrow in order to confront a shortfall in the trillions of dollars, saying, "I will not prejudge any solution."

But, he said, "We will not raise payroll taxes to solve this problem."

Bush spoke after meeting in the Oval Office with the Social Security trustees who submit an annual report on the state of the program's funding.

His decision to rule out raising payroll taxes will hurt efforts to get support from moderate Democrats opposed to government borrowing at a time of record-breaking budget deficits.

Some Republicans have said they would consider raising or removing the limit on income subject to the 12.4 percent payroll tax split between workers and employers. The maximum level of earnings taxed is $87,900 now; it will rise to $90,000 next year.

Sen. Lindsey Graham, R-S.C., has said he would consider lifting the cap if his plan would get bipartisan support. Sen. Charles Grassley, R-Iowa, chairman of the tax-writing Senate Finance Committee, also has said tax increases should be considered.

Social Security today collects more in taxes than it pays out in benefits. The extra money is used to buy Treasury bonds from the government. The government then spends the money as part of its general revenue. The system will start paying out more in taxes than it collects in benefits in 2018.

Estimates of the money needed to keep the system solvent range from $1 trillion to $2 trillion or more over a decade. Bush said the total unfunded liability is $11 trillion.

"The question is, does this country have the will to address the problem? I think it must. I think we have a responsibility to solve problems before they become acute," Bush said, sitting next to Treasury Secretary John Snow (search) and other trustees.

"There is a recognition among the experts that we have a problem, and the problem is America is getting older and that there are fewer to pay into the system to support a baby boomer generation which is about to retire," Bush said.

The call for private accounts is the most controversial element of Bush's vision for a remodeled Social Security.

A presidential commission in 2001 proposed allowing individuals to place up to 2 percent of their payroll into a private account to be invested for retirement. Any such plan depends on a large infusion of cash to replace the tax money that would otherwise fund the government benefits.

Bush and lawmakers of both parties generally agree on the need for eventual changes in Social Security to shore up its solvency. But they disagree sharply on the urgency of the task and the wisdom of letting workers channel a portion of their payroll taxes into private accounts.

Workers generally pay a 6.2 percent payroll tax on income up to $87,900. Their employers match the payment, and the combined tax finances monthly Social Security retirement checks.

Apart from borrowing, another option for covering costs is to increase the retirement age, which is gradually rising to 67 under legislation approved nearly two decades ago.

Bush wouldn't say how he would pay for the changes.

"I have articulated principles in the course of my campaign that I think are important, and it's very important for those who have retired to recognize that nothing is going to change when it comes to Social Security," Bush said.