Ryan has been studying issues -- and opponent

WASHINGTON -- To prepare for his biggest test yet on the national stage, untested debater Paul Ryan has been hauling two thick briefing books around the country and intently studying up on Vice President Joe Biden, who has been sparring over public policy since the Wisconsin congressman was learning how to talk.

Ryan, the 42-year-old Republican vice presidential nominee, has suggested his age will be an asset in connecting with voters at the sole vice presidential debate tonight in Kentucky against the 69-year-old former senator.

But risks abound for the GOP rising star, who hasn't participated in a campaign debate since his first run for office 14 years ago.

The main goal for Ryan's inner-circle: get him comfortable answering questions in broad terms that connect with voters.

Ryan's team wants to keep him on point about positive changes a Romney-Ryan administration would mean for the country.

As the House Republicans' top budget writer, aides say Ryan is confident he can handle questions about federal spending and taxes.

He is a bit more nervous on international affairs -- an area in which he has limited exposure since being thrust into the national spotlight two months ago.

Ryan has spent hours huddling with advisers to polish his delivery and has been cramming with aides to sharpen his grasp of foreign policy and national security issues.

He has watched video of Biden's 2008 vice presidential debate and recent campaign appearances. He knows Biden's cadences and verbal ticks.

Ryan and his aides also are trying to play up the vice president's skills and perhaps set unrealistic expectations for Biden before their one and only meeting in Danville, Ky.

"Joe Biden's been doing this for 40 years," Ryan told a Milwaukee radio station. "I mean, the man ran for president twice, he's the sitting vice president. And this is my first time on this kind of stage. So sure, there's a lot of pressure."