Paul Ryan prepares to take on skilled debater Joe Biden Thursday

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 youth will be an asset in connecting with voters at the sole vice presidential debate Thursday 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 and avoid the wonky, in-the-weeds answers more appropriate for a budget hearing than a living room.

Ryan's team wants to keep him talking about positive changes a Romney-Ryan administration would mean for the country, not a full-throated defense of the campaign's sometimes nebulous math.

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 — and for good reason. Ryan was thrust into the national spotlight a few months ago when he joined the Republican ticket but has limited exposure in that arena.

Biden is a former chairman of the Senate Foreign Relations Committee and a skilled debater, both within the administration and against its critics, and someone whose opinion President Barack Obama seeks out on major decisions.

Ryan also is bracing for Biden to try to help Obama overcome a rough patch by staking out an aggressive tone.

"I really think that because they had such a bad debate that Joe is just going to come flying at us," Ryan said this week.

His biggest worry: looking unprepared the way his mentor and former boss, Jack Kemp, did in the 1996 debate against Vice President Al Gore.

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. As they prepared in Virginia's mountains about 150 miles from Washington, Ryan focused on trying to shoehorn knowledge gained from seven terms in the House into two-minute answers. He has watched video of Biden's 2008 vice presidential debate and recent campaign appearances. He knows Biden's cadences and verbal ticks, including the signature "ladies and gentlemen" and punchy "folks" to get the audience's attention.

Ryan also has spent time working on trying to keep Biden from cutting him off, talking over him or throwing a wrench into his rehearsed answers. During practice debates, his stand-in for Biden, former Solicitor General Ted Olson, has been aggressive in trying to throw Ryan off his game.

"He's learning how to debate," said Michael Steel, Ryan's traveling spokesman who was a top aide to House Speaker John Boehner. "It's not about learning policy. ... It's about learning how to debate at this level."

Ryan and his aides also are trying to play up the vice president's skills and perhaps set unrealistic expectations for Biden, who is doing his own cram sessions in Delaware before the meeting in Danville, Ky.

"Joe Biden's been doing this for 40 years," Ryan told WTMJ-AM radio in Milwaukee. "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."

He later seemed to suggest that his youth gave him the upper hand.

"I've been in Congress 14 years. I'm a younger person. I'm next generation," he told WTOL in Toledo, Ohio. "I'm in my 40s. Joe Biden is in his 60s. I'm used to debating people in Joe's generation in Congress."