Mr. Santorum said his proposal for a zero percent corporate tax rate on manufacturing would bring jobs back to small-town America.

In highlighting who would benefit from competing Republican tax proposals, Mr. Santorum seemed to be using urban-rural rivalry as a way to suggest that Mitt Romney, one of his opponents, was the candidate of more liberal city dwellers and that he was the candidate of more conservative rural residents, though polls show that Mr. Romney tends to do well in suburban areas.

At a rally on Friday morning in Osage Beach, Mo., Mr. Santorum complained about “all of the experts and pundits” who say that “we’ve got to elect someone who’s more moderate, someone who can appeal to moderates and independents in New York City and Los Angeles” and “Wall Street and corporate boardrooms” — groups whose mention drew boos from many in the audience of about 500.

He told the crowd that an analysis — he did not say whose — showed that he had “won 60 percent of the counties throughout the entire course” of the Missouri contest.

“And if you look at where my Republican opponent has won, it’s always in and around the cities,” Mr. Santorum added, in what seemed to be a clear reference to Mr. Romney, whom he did not mention by name.