Five-term Rep. Jeff Miller (R-Fla.), who represents the Panhandle-based 1st district, announced Thursday that he is backing former state Speaker Marco Rubio (R) in the Sunshine State’s 2010 Senate primary.

Miller is the first Member of the Florida delegation to come out for Rubio, and his endorsement puts him on the opposite side of national party leaders — who have lined up behind Gov. Charlie Crist (R) in the race.

Geography is important in Miller’s endorsement. While Crist is well-known and popular statewide, Rubio needs to demonstrate that he can gather support outside his South Florida base.

“Marco Rubio possesses an impressive combination of idea-driven, principled leadership and the ability to communicate conservative values in ways that resonate at the kitchen table,— Miller said in a statement released by Rubio’s campaign. “Americans deserve better than the current big government, borrow-and-spend road we are on, and I believe Marco Rubio will be a compelling voice to lead us to a stronger and more prosperous America.—

Like Rubio, Miller is a social and fiscal conservative. While still considered the underdog in the race, Rubio has been buoyed in recent weeks by the endorsements of big-name conservatives from around the country, including former Arkansas Gov. Mike Huckabee.

Crist has earned endorsements from retiring Sen. Mel Martinez (R-Fla.), who he and Rubio hope to replace next year, the National Republican Senatorial Committee, Senate Minority Leader Mitch McConnell (Ky.) and the rest of the Senate’s top GOP leadership.

While Rep. Ileana Ros-Lehtinen (R-Fla.) has said she is staying on the sidelines in the primary, the Miami Herald reported last week that the Congresswoman’s husband, former U.S. Attorney Dexter Lehtinen, will host an upcoming fundraiser for Rubio. Rubio once worked in Ros-Lehtinen’s office as an intern.