The 18-year-old darts sensation has taken the number one slot in the rankings from his rival and knows the pressure will be on from his friend wanting to regain his crown.
Littler - who cemented his placing by beating Humphries in the Grand Slam of Darts final at the weekend - told Sky Sports: "It definitely is war because if someone obviously takes it off you, then you want it back. You don't want to be second.
"It's taken me 19 to 20 months to get to world No 1, so now I want to stay there for a few years.
"Luke was an incredible world No 1. He won plenty of titles along his way and he kept that gap from me.
"But I won many more to close the gap and now I've finally closed the gap. I've overtaken him, but now he wants it back and I've got to make sure that I'm on my game if we ever do meet in another final."
And Humphries is hopeful he can triumph in the World Darts Championship, which stars at London's Alexandra Palace next month.
He said: "I'm ready for the Worlds now. I'm going to win the Worlds.
"I am [declaring war] because I'm obviously disappointed to lose last three finals, but I'm playing good, and the tiredness crept in at the end there.
"One game a day suits me. We're going to go to war. World Championships, me and him in a final. We're going to see who's the number one there."
Both players agree they are "elevated" above the other darts players in competition and called for new challengers.
Littler said: "I think we are.
"The finals show it, the stats show it and if everyone's getting bored of me and him, then someone needs to stop us, otherwise we're going to keep winning.
"We're always going to meet in the final if we get past our opponents and we'll make it continue.
"Now I've got that No 1 spot, obviously he wants it back, but now we're going to be battling even more.
"I think we're going to keep playing well because he wants it back and obviously I don't want to give it away.
"You're going to see many more great games."
And Humphries said: "Honestly, I do. I'm not being arrogant when I say that.
"I feel like a lot of people get a little bit just complacent and say it's another Luke v Luke final or it's rubbish. But what can we do?
"We're opposite sides of the draw and we keep meeting each other. I mean, people can stop us, it's up to them.
"It's up to everyone else to stop us, and if they do, good luck to them. But at the moment, me and Luke are playing a level of this sport that's better than everyone else.
"We're going to keep competing finals. Regardless of what happens with the world No 1, I want to be in the world final with him.
"We want to go again, toe to toe and see what we got, baby."
