Washington ? In the arsenal of the culture wars, rap music remains somewhat radioactive – and Barack Obama now finds himself exposed.

Avowed Obama supporter Ludacris lat month released a freewheeling song called “Politics” in which he repeatedly praised the candidate – as well as himself, for having found a home on the senator’s iPod. But the Atlanta rapper also used a derogatory term to describe Hillary Clinton; asserted that John McCain should be in a wheelchair, not the White House; and declared that President Bush “is mentally handicapped.”

Gee, thanks for the endorsement, Luda!

Some of the Democrat’s most vocal (literally) supporters are sticking him with a hip-hop dilemma: how to respond to an art form that has a long history as a cultural wedge issue but whose fans and wildly unpredictable practitioners are a part of his base?

Rappers tend to love him – or at least the basic idea of a black man in the White House. Pro-Obama rap songs and references are proliferating at a staggering clip, and online video endorsements are arriving just as quickly, from “Yes We Can” splicer Will.I.Am and hip-hop impresario Sean “Diddy” Combs on down.

But Obama can’t love them back – at least not unconditionally, given the music’s continuing lightning-rod status. This is a man, after all, who has worked tirelessly to make inroads among older white voters, many of whom have a deep aversion to hip-hop.

Whenever Obama is asked about rap music in interviews, he always tempers his praise.

“I love the art of hip-hop; I don’t always love the message of hip-hop,” he told BET earlier this year. “There are times where even … with the artists I love, you know, there’s a message that is not only sometimes degrading to women; not only uses the n-word a little too frequently; but – also something I’m really concerned about – it’s always talking about material things.”

Likewise, the Obama campaign immediately denounced “Politics” and suggested that “while Ludacris is a talented individual, he should be ashamed of these lyrics.”

Obama is the first viable presidential candidate with an acknowledged affinity for hip-hop culture, having spoken fondly of Kanye West, Jay-Z and, yes, Ludacris. He borrowed Jay-Z’s dirt-off-my-shoulder gesture to brush off his “haters” during a much-analyzed April speech that was loaded with the sort of swagger that’s typical of hip-hop.

Obama’s candidacy is like catnip to rappers. Traditionally ambivalent about electoral politics, this time around they are drawn to the senator’s rhetoric, the historic nature of his bid, or maybe just the rhyming possibilities of his name, as with a remix of Ice Cube’s “Gangsta Rap Made Me Do It,” on which Scarface raps: “I hope that Barack could pull the troops from Iraq.”