Gov. Rick Perry of Texas on Tuesday offered his most detailed response yet to criticism that he views Social Security as a Ponzi scheme, spelling out changes to the federal retirement program that he said would “save Social Security for future generations.”

Mr. Perry came under fire almost as soon as he joined the presidential race this summer for saying in a recent book that Social Security was a “fraudulent system” and comparing it to a Ponzi scheme.

“This unsustainable fiscal insanity is the true legacy of Social Security and the New Deal,” Mr. Perry wrote in his book, “Fed Up!”

Mr. Perry’s Republican rivals seized upon the comments in news releases, speeches and during debates. For weeks, Mr. Perry stood by his book, refusing to disown the “Ponzi scheme” description and insisting that he was the only one willing to speak the truth about the program.

But in a speech at a film factory in South Carolina, Mr. Perry on Tuesday sounded a much more admiring tone when it came to the popular federal benefit.

“I am putting forward five principles to save Social Security for the long-term,” Mr Perry said, echoing the language of his rivals on the campaign trail.

Mr. Perry said his plan would not affect current retirees or people nearing retirement. He vowed to stop “pillaging” the Social Security Trust Fund. And he proposed allowing young workers to invest a portion of their payroll tax in private accounts, a standard Republican idea.

“The liberals think the American people cannot be trusted to safeguard even a portion of their own retirement dollars,” Mr. Perry said. “It is time to end the nanny state and empower our people to exercise greater control over their money.”

Mr. Perry repeated his idea that states should be given the freedom to allow their government employees to opt out of the program for something better. And he said he would “work with Congress” to raise the retirement age for younger workers.

“This is common sense, and it can help save Social Security for future generations,” he said.

Nowhere in the speech did Mr. Perry again suggest that Social Security was a “Ponzi scheme.” Though he did assert that if “we don’t act, in 25 years benefits will be slashed 23 percent overnight.”

But the overall tone was aimed not at criticizing the program, but at a desire to save it.

“Protecting Social Security benefits begins with protecting the solvency of the fund, and stopping all current borrowing from the fund, just as we have done with the highway trust fund,” Mr. Perry said.