WASHINGTON - Senator Marco Rubio of Florida on Wednesday endorsed former Massachusetts governor Mitt Romney for the Republican presidential nomination during an appearance on Fox News.

Rubio said Romney has "earned the nomination" and offers a "very clear alternative" to Democratic President Barack Obama.

"I am endorsing Mitt Romney and the reason why is not only is he going to be the Republican nominee but he offers at this point such a stark contrast to the president's record," Rubio said.

Rubio, a first-term senator and rising Republican star, again played down speculation he might accept the second spot on his party's presidential ticket.

"I don't believe I'm going to be asked to be the vice presidential nominee," he said, adding it was not something the he desires.

(Reporting By JoAnne Allen; editing by Todd Eastham)