WASHINGTON — President Bush stepped up his campaign to partially privatize Social Security yesterday, hosting a talk-show-style conversation with supporters of a plan to allow participants to funnel a portion of their payroll taxes into private investment accounts.

Bush said his plan would bolster an outmoded Social Security system that he described as careening toward insolvency.

"If you're ... in your mid-twenties, and you're beginning to work, I want you to think about a Social Security system that will be flat bust, bankrupt, unless the United States Congress has got the willingness to act now," he said.

Bush also claimed an election mandate to change the entitlement program for the retired.

The president warned members of Congress, some of whom have voiced deep skepticism about his plan, that they could face dire political consequences if they do not address Social Security.

"I happen to believe people who have been elected to office who ignore problems will face the price at the ballot box," he said.

But some critics say Bush is exaggerating the Social Security problem to build support for his plan. They say the term "bankrupt" does not apply to Social Security. If nothing is done to the system, Social Security could still pay about 73 percent of promised benefits in 2042, when the system's trust fund of Treasury bonds will be depleted, Social Security's chief actuary has calculated.

Even after adjusting for inflation, that 27 percent cut in benefits would leave monthly Social Security checks considerably higher than they are now. If nothing is done, a worker retiring in 2055 would receive first-year benefits totaling $16,700 in today's dollars, considerably less than the promised $21,600 but more than today, according to the Congressional Budget Office.

"The Social Security tax collects 12.3 percent of the wages each year. That money is going to be available to pay benefits," said Bernard Wasow, a senior fellow and economist at The Century Foundation. "That's not bankrupt."

Although Bush touted the benefits of private accounts, he did not talk about the significant costs — an estimated $2 trillion — of establishing them. He also did not mention the steep cuts in guaranteed benefits that experts say are sure to accompany his plan.

The White House has pointed out that Social Security is projected to start paying out more in benefits than it collects in taxes in 2018. Although it can then dip into its substantial reserves, the system can pay promised benefits only until 2042. To bridge the gap, White House officials have focused on a plan that would change how future benefits are calculated by tying them to price changes rather than wage changes, which would most likely result in significant cuts in future benefits.

"Who campaigned on price indexing? Who campaigned on cutting future benefits? They campaigned on personal accounts. It's a bait-and-switch to say now we're going to go to [benefit cuts] price indexing," said Peter Ferrara, a conservative Social Security analyst.