"You can't take it to the race track and hope to really increase the returns. It's not there for the lottery," said Mr. Bush, speaking on the second day of a conference called to promote the administration's economic agenda.
He compared the planned structure of the private Social Security accounts to an investment plan available to federal workers - the Thrift Savings Plan, a tax-deferred retirement investment plan similar to a 401(k).
"There will be reasonable guidelines that already exist in other thrift programs that will enable people to have choice about where they invest their own money, but they're not going to be able to do it in a frivolous fashion," said the president.
Investments are not without risk, as seen by the Thrift Savings Plan's annual returns. Federal workers have five investment options, including government and corporate bond funds, a stock fund that tracks the S&P 500, an international fund and other stock funds.
The stock funds performed well in the 1990s, with annual returns ranging from 20 percent to 43 percent. But in the 2001 recession and later, they have posted annual losses as high as 22 percent. Over 10 years, all the funds were profitable.
Thursday, Mr. Bush appealed for congressional action to shore up the system and said lawmakers supporting him would not be risking their seats.
"This is an issue on which I campaigned, and I'm still standing," said the president.
Advocates of Social Security reform have predicted the program will go into the red in the year 2018. CBS News Radio Correspondent Mark Knoller reports Mr. Bush is declaring the crisis is now and that's the case he will make to members of Congress.
"You may not feel it," Mr. Bush said. "Your constituents may not be overwhelming you with letters demanding a fix now. But the crisis is now."
Not invited to this week's White House conference on the economy are some prominent critics of the Bush Social Security reform plan.
They include AFL-CIO President John Sweeney, who calls the Bush Social Security plan "a risky scheme for America, but a sure bet for the financial services industry."
Standing with Sweeney Thursday in opposition to the Bush plan were representatives of the NAACP, the National Organization for Women, and the Alliance for Retired Americans, at a Washington news conference organized by the Campaign for America's Future, a self-described progressive group active on economic issues.
In a letter to the Securities Industry Association, Sweeney calls on investment industry leaders to disavow President Bush's approach.
"Will the financial services industry behave as professionals with a duty to speak candidly to the investing public," Sweeney writes, "or will elements of the industry once again seek to make money at the expense of their customers, only this time on a much grander scale?"
Liz Ann Sonders, a participant in the Bush economic conference, takes issue with the idea that the Social Security reform plan would be a case of Wall Street making money at the expense of the public.
"The fees are structured to be so minimal that in fact, even the studies have show that under any set of proposals, Wall Street doesn't make any money on this for another seven or eight years," says Sonders, chief investment strategist for the Charles Schwab brokerage firm.
Another critic of the Bush plan disagrees with estimates on when the Social Security system will run into trouble.
In a New York Times interview, Mark Weisbrot of the Center on Economic Policy Research - a liberal research group - says the Social Security system is in no worse financial condition than it has been at most points in the past few decades.
"This whole idea that Social Security needs to be fixed is false," says Weisbrot, who contends that the program should be able to pay full benefits for at least 38 years.
President Bush's comments on Social Security came Thursday on the second day of a conference called on economic issues on the front burner for Mr. Bush's second term of office, including tax cuts, trade and the weak dollar.
The president and his economic team are trying to get the jump on Democrats and lobbying groups before the congressional Social Security debate heats up early next year.
The president credited his tax-cutting policies with reviving the economy. Mr. Bush said his strategy will be "to grow the economy with reasonable tax policy but to make sure the deficit is dealt with by being wise about how we spend money."
"It's not going to be easy," the president said. "It turns out [congressional] appropriators take their title seriously."
Addressing concerns about the record budget deficit, President Bush also promised to send Congress "a tough budget" early next year to hold the line on spending.
"You will see fiscal discipline exercised inside the Oval Office this coming budget cycle," the president told the economic conference.
Economists and baby boomers approaching retirement are not the only ones monitoring the debate on Social Security. CBS News Correspondent John Roberts reports that recent college graduates, who might be the most affected by a new plan, are keeping an eye on the proposed legislation.
"To change this one thing, to see a temporary fix, is not the solution, because in the long run it might be very helpful, but it also might be very hurtful," Ahmed said.
Thursday, one of Bush's panelists talked about the resiliency of the U.S. economy and noted the unreliability of the financial markets.
"Everybody knows we faced an incredible number of shocks in the last several years. These shocks, which, by the way, destroyed almost half of the stock's market value in a short period of time," said James Glassman, senior economist with JP Morgan Chase.
The shocks, including the 2001 terrorist attacks and the corporate accounting scandals, "were potentially as devastating as the shocks that triggered the Great Depression," he said. "And yet, the experts tell us the recession we just suffered in the last several years was the mildest recession in modern times."
Supporters of personal accounts argue that if the system is not changed, future retirees will not get the benefits being promised today. Though going to a system of investment accounts means the government would cut promised benefits, participants theoretically could make up the difference through their investments.
"This result is superior, particularly compared to the returns you would get leaving that money with the government," said Richard Parsons, chairman and chief executive of Time Warner Inc. and co-chairman of the 2001 Presidential Commission to Strengthen Social Security.
"People ought to be able to start to save on their own behalf to create wealth for themselves so that they have that wealth to look to in their later years, as opposed to a government promise only, which at some point in time is going to have to come up empty," he said.