Giuliani drew applause dozens of times as he told the anti-tax group Americans for Prosperity how he cut income and business taxes, slashed welfare rolls and trimmed employees from his city's payroll as mayor of New York.
"We lost control of Congress because we were just like the Democrats as far as spending is concerned - shame on us," Giuliani said. But he added, "Republicans are amateur spenders, and Democrats are professional spenders."
His record on taxes is an advantage for Giuliani, who is at odds with social conservatives who typically hold sway over Republican primary elections.
Yet fellow GOP hopefulargues Giuliani is vulnerable on taxes because the former mayor fought to eliminate a line-item veto, which a president can use to reject spending, and because Giuliani maintained a commuter tax in New York.
The issue sparked a pointed exchange Thursday, as Giuliani's campaign responded that Romney offered no tax cuts during his four years as Massachusetts governor.
Romney started running a new radio ad Friday in New Hampshire telling voters he has signed a pledge not to raise taxes. He was scheduled to address the anti-tax group Friday evening, as was former Tennessee Sen. Fred Thompson.
Other GOP hopefuls - former Arkansas Gov., Kansas Sen. and Texas Rep. - also addressed the group.
Brownback argued for fixing Social Security with private savings accounts, saying, "if the money is in personal accounts, the government can't spend it."
Giuliani, who leads the GOP presidential field in most national polls, spent most of his 25-minute speech ridiculing Hillary Rodham Clinton and other Democratic candidates. Clinton, Barack Obama and John Edwards would pay for their more costly proposals by repealing tax cuts.
Clinton's idea of giving a $5,000 savings bond to every U.S.-born baby drew laughter from the group's members, who wore name tags with Ronald Reagan's picture on them. Giuliani said the price tag would be more than $20 billion and joked about the cost of printing bonds with Clinton's picture on them.
"This costs money - it doesn't come from trees; it doesn't come from heaven," Giuliani said.
Giuliani argued for indexing the alternative minimum tax to inflation and repealing the estate tax, saying the tax reductions would actually generate tax revenues and not cost money because they would stimulate the economy.
By the time he left office as mayor, Giuliani said, "we were collecting 41 percent more revenue from the low taxes than we were collecting from high taxes."