WASHINGTON—Sen. Marco Rubio put forward a simple recipe for the country in his response to the president's State of the Union address: Stir economic growth, and you will fix the middle class. And if you fix the middle class, you will assure the country's strength.

Picked by his party to deliver the official response to Mr. Obama's address to Congress, Mr. Rubio gave his speech in an earnest, sometimes jittery fashion in front of a window overlooking the Capitol.

In all, the speech appeared unlikely to do the Florida senator much good or much harm, as has been the case for most who have given similar responses since the tradition began in 1966.

In a 2,500-word address that was a sort of miniature State of the Union address in its own right, Mr. Rubio mentioned the "working class" and the "middle class" 17 times. President Barack Obama, in a speech more than twice as long, mentioned the middle class six times.

As expected, Mr. Rubio made much of his humble origins as the son of Cuban immigrants who grew up in a working-class neighborhood of Miami and still lives there. Addressing Mr. Obama, he said, "So Mr. President, I don't oppose your plans because I want to protect the rich. I oppose your plans because I want to protect my neighbors."