WASHINGTON - US Senator Marco Rubio, seeking to help the Republican Party shed its image as a defender of the rich, planned to stress his working-class upbringing and the need to save social safety net programs during his response on Tuesday to President Barack Obama's State of the Union address.For Rubio, 41, the speech represented a potential star-making moment at a time when Republicans are desperate to reach out to the nation's fast-growing Latino population, which voted overwhelmingly for Obama and Democrats in the November elections.Excerpts of Rubio's remarks released before he spoke indicated that the first-term senator from Florida would stress his modest upbringing as a son of Cuban immigrants - and that he would strike working-class themes that are staples of speeches by Obama and other Democrats.