DETROIT--In what his campaign billed as a major economic speech, Mitt Romney sought to boost his conservative credentials by pledging "more jobs, less debt and smaller government" if he is elected president.

Criticizing President Barack Obama's handling of the economy, Romney said in a speech delivered from the 30-yard line of Ford Field, the home of the NFL's Detroit Lions, that he is "offering more than just a change in policy" from the current administration.

"I am offering a dramatic change in perspective and philosophy," Romney said.

The speech largely summarized and reiterated the economic message that Romney has put forward during his presidential campaign. He proposed cutting individual marginal income tax rates by 20 percent; reducing the corporate tax rate to 25 percent, from 35 percent; eliminating capital gains taxes for people with incomes below $200,000; abolishing the alternative minimum tax and the estate tax; indexing the eligibility age for Medicare to longevity; allowing private insurers to compete with Medicare; eliminating the Affordable Care Act, Obama's health care law; and reducing federal spending to 20 percent of the national economy by making "hundreds of billions of dollars in cuts," including to programs like Amtrak and Planned Parenthood.

Romney received an instant avalanche of criticism on Twitter after the speech for saying of his wife's affection for American cars, "Ann drives a couple Cadillacs, actually." (A Cadillac SRX, a campaign spokesman later confirmed. She has one at their home in California and another in Massachusetts. Mitt, for his part, owns a Ford Mustang and a Ford truck.)

He gave a special emphasis in the speech to Michigan, where his late father was once a beloved governor and where he is in a close race with Rick Santorum heading into Tuesday's primary. He said he would work to make Detroit not just the "motor city of America" but the "motor city of the world."

Romney has been slowly revealing the details of his economic proposals for months. The real purpose of Friday's speech was to answer critics who say he hasn't explained how he would carry out conservative policies as president.

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"Their effort to prove he's conservative so far has been for him to deliver a speech where he says 'conservative' or 'conservatism' a million times," a Republican strategist close to the Romney campaign told Yahoo News. "There's been no policy that demonstrates that conservatism."

In some ways, the speech was overshadowed by the unusual setting.

The Romney campaign, which did not pick the venue, sought to downplay the stadium setting by telling reporters that it would not be full for the candidate's address. As Romney spoke to 1,200 members of the Detroit Economic Club, the cavernous stadium seemed to eat up all the sound from the event, making the audience's warm applause seem less enthusiastic. Throughout his speech, Romney's voice echoed throughout the stadium, highlighting its emptiness.

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