David Goldman/Associated Press

Herman Cain, who made his fortune pitching soda, burgers and pizza before turning to politics, declared himself a candidate on Saturday for something that few others seem to want these days: the Republican nomination for president in 2012.

At a noontime rally at a park in Atlanta, his hometown, Mr. Cain, 65, whose conservative fiscal credentials have made him a favorite among some Tea Party backers, promised “a real vision” to confront the nation’s growing economic and foreign policy problems.

And he vowed to prove wrong the “doubting Thomases” who regard him as a long shot. “I’m not running for second!” he shouted to cheers from several thousand supporters, as he laid out “the Cain doctrine” for promoting economic growth and protecting national security.

In a stylish video that accompanied his announcement, Mr. Cain offered few specific proposals but instead relied on sweeping, Reaganesque themes and allusions to God’s role in America as he promised what he called “a new American dream.”

“We can turn this country around,” he said. “We will make this country great again.”

Mr. Cain, who has never held public office, hopes to leap headlong into a Republican race that is as notable for who is not running as who is.

Big names like Mike Huckabee, the former Arkansas governor; Gov. Haley Barbour of Mississippi; and Donald J. Trump, the businessman and reality TV star, recently announced that they would not seek the Republican nomination to run in the general election next year against President Obama.

Sarah Palin, a former governor of Alaska, has yet to declare her intentions. But the rest of the field is slowly coming together. Tim Pawlenty, a former governor of Minnesota, is scheduled to declare his candidacy on Monday in Iowa. Mitt Romney, a former governor of Massachusetts, has opened an exploratory campaign and is aggressively raising money. Jon M. Huntsman, a former Utah governor and United States ambassador to China, is considering entering the race and Gov. Mitch Daniels of Indiana has said he will announce his plans soon.

While other possible contenders have skipped many of the early events this year, Mr. Cain has been aggressively crisscrossing the country and trying to build name recognition among a public more familiar with the company he once ran, Godfather’s Pizza, than with the candidate himself.

A graceful public speaker with a deep baritone voice, Mr. Cain has spoken at dozens of Tea Party rallies. In March, he attended a forum in Iowa that marked his informal kickoff to win the state’s delegates, and he was one of just five second-tier hopefuls who took part in a Republican presidential debate in South Carolina this month.

Mr. Cain’s early supporters are hoping that his plainspoken speaking style, his up-from-the-bootstraps life story, and his success in business will appeal to conservative voters.

The son of a chauffeur and a domestic worker in Georgia, he graduated from Morehouse College, a historic black college, with a degree in mathematics, and he earned a master’s degree at Purdue before joining the Navy. He then began his rise in the corporate world, first at Coca-Cola and then at the Pillsbury Company, where he was an executive overseeing Burger King and chief executive at Godfather’s Pizza.

His first venture into national politics was almost accidental. At a nationally televised town hall meeting in 1994, he challenged President Bill Clinton‘s health care plans and their potential effect on businesses. When Mr. Clinton assured him that the proposal would not harm businesses, Mr. Cain answered that “in the competitive marketplace, it simply doesn’t work that way.”

He used his newfound prominence among conservative groups to become more outspoken in politics, hosting a radio show in Atlanta, writing books on political themes and losing a 1994 Republican primary for the United States Senate in Georgia.

Nearly two decades after his televised run-in with Mr. Clinton, Mr. Cain will probably use his opposition to President Obama’s health care plan as one focal point of his campaign in railing against what he called “an out-of-control federal government that spends recklessly, taxes too much and oversteps its constitutional limits far too often.”

At Saturday’s rally, he also pledged to cut corporate tax rates and make permanent the tax breaks enacted under President George W. Bush. He also said he would push for new energy policies to make the United States less dependent on foreign oil, protect Israel’s interest in the Middle East and pursue tougher immigration policies to secure American borders.

He drew perhaps his loudest cheers when he praised Arizona’s controversial immigration law, which gives state officials more power to move against suspected illegal immigrants, and condemned the Obama administration’s decision to sue the state over the law.