ON TV, Bill O’Reilly and Sean Hannity are shoulder-to-shoulder teammates on Fox News Channel – on radio, however, they are going head-to-head starting today.

O’Reilly kicks off “The Radio Factor” at 3 p.m. on WOR (710 AM) – directly opposite Hannity’s show on WABC (770 AM).

Elsewhere around the country, O’Reilly – the No. 1 talk show host on prime-time cable and a best-selling author – will be going up against conservative talker Rush Limbaugh.

But because of a quirk of scheduling in New York, O’Reilly’s show airs from 3 to 5 p.m. – directly opposite Hannity’s show from 3 to 6 p.m.

Hannity’s mug has suddenly popped up all around town in a pricey billboard and bus-side ad campaign. And WABC is sponsoring a contest where Hannity’s listeners can win a Jeep and cash.

“It’s clearly an attempt to blunt the impact of O’Reilly,” says John Mainelli, WOR’s general manager. “The buses used to have all [WABC] personalities, now they have just Sean.”

WABC program director Phil Boyce doesn’t disagree – but says the Hannity marketing push was planned.

“Obviously, it has something to do with [O’Reilly], but not everything,” he says. “We normally get involved in a spring campaign, and this year we thought it was a good idea to take care of Sean this time around.”

Adding fuel to the fire: A report published yesterday by Internet gossip columnist Matt Drudge, saying that Westwood One, which syndicates O’Reilly’s show, is paying stations (including WOR) up to $300,000 to carry O’Reilly’s show.

“WOR does not discuss contracts or deals,” Mainelli said.