There’s a dark secret behind the bitter feud between late-night TV rivals Jay Leno and David Letterman: Malicious guests and rival staffers are keeping the nasty quarrel alive!

“There are people out there who enjoy promoting jealousy and animosity between Jay and Dave,” says a friend of Leno. “Jay would like to be friends, but it’s nearly impossible because Dave believes a lot of the bad stuff he hears about Jay.”

The troublemakers find it easy to goad “Late Night” host Letterman, who has resented his rival ever since Leno beat him out for the “Tonight” show spot vacated by Johnny Carson a decade ago, sources say. To make matters worse, Leno regularly whips Letterman in the ratings.

“There are people at CBS who feed Dave stories about how Jay’s supposedly trashing him because he’s in second place in the ratings war,” a source close to Letterman said. “The network TV people do this because they think it keeps Dave on his toes and makes him try harder for a better show.

“Celebrity guests sometimes resent the caustic way Dave can treat them on the air and they tell him that Jay thinks he’s a big jerk and loves the fact that he’s killing Dave in the ratings. Even Dave’s own staffers carry tales to him supposedly picked up from their opposite numbers on Jay’s show — like how Jay thinks Dave’s overpaid considering the ratings he gets.

“Dave gets paranoid about this stuff; he doesn’t realize he’s being manipulated by people who like to cause trouble.”

Angry Letterman takes revenge for these rumored slights by dissing his rival on the air, as he did when he joked on Father’s Day that one sign your kids hate you might be “instead of watching Daddy’s show, they watch that hump Jay Leno.” Leno tries not to react to these assaults because he wants to cool things down, sources say, and he insists he doesn’t talk about Dave behind his back.

“Jay thinks Dave’s nuts to take this stuff seriously and actually believe it’s true,” said the friend of Leno’s.

“There are people out there fanning the flames and he knows their game and thinks it’s stupid. He just wishes Dave would wise up to their nastiness, too.”