By Eric Johnson

CHICAGO — Vice President Joe Biden, in his first public criticism of a 2012 Republican presidential candidate, criticized Mitt Romney’s economic policies in an opinion piece in Iowa’s biggest newspaper on Friday.

“Romney appears satisfied to settle for an economy in which fewer people succeed, while the majority of Americans are left to tread water or fall behind,” Biden wrote in the Des Moines Register, which last week endorsed Romney for the Republican nomination.

In the piece, Biden laid out his working-class background — which the Obama campaign will tout in rust-belt swing states in 2012 — and said he and Obama were champions of equal opportunity for all, not an entitlement society, as Romney alleged.

“The president and I firmly believe…that if you work hard and play by the rules, no opportunity should be out of reach,” he wrote. “That is a fundamentally different vision than what the other side has proposed.”

The jabs jibe with the Obama campaign’s focus on the former venture capitalist they see as Obama’s most likely challenger. They also provide a taste of what’s to come in a hotly contested general election.