President Bush on Thursday signed new rules to prod companies into shoring up their pension plans with a tough message for corporate America: "Set aside enough money now."

Before an enthusiastic audience in an office building on the White House grounds, Bush called the legislation "the most sweeping reform of America's pension laws in over 30 years."

"Americans who spend a lifetime working hard should be confident that their pensions will be there when they retire," Bush said. "Some businesses are not putting away the cash they need to fund the pensions they promised to their workers."

The massive legislation reflects the evolution of workers' retirement benefits — the decline in traditional pensions that give retired employees a fixed payment each month and the rise of defined-contribution savings plans that rely on workers to build retirement assets.

It could also save taxpayers from funding a multibillion-dollar bailout of the federal agency that insures pension plans.

Some critics, such as the Pension Rights Center, say the changes do nothing to stop companies from freezing their pensions and, with time, will weaken the pension system.

Bush seemed to recognize that, and urged companies to do their part on their own.

"This bill establishes sound standards for pension funding," he said. "Yet in the end, the primary responsibility rests with employers to fund the pension promises as soon as they can. The message from this administration, from those of us up there today, is this: you should keep the promises you make to your workers. If you offer a private pension plan to your employees, you have a duty to set aside enough money now so your workers will get what they've been promised when they retire."