Caulker moved to Wales from Tottenham a year ago and played in every minute of Cardiff's miserable Premier League campaign, which ended in relegation.
He was handed his Spurs debut by Redknapp, and a reunion with the QPR boss now looks likely.
His imminent arrival follows the signing of Rio Ferdinand on a free transfer and Redknapp was also happy to discuss an array of other potential arrivals into west London.
"We've agreed a fee with Cardiff for Steven Caulker," he said.
"He's got a couple of other clubs interested in him but I'm hoping to get that one done. I mean the chairman's been pushing it and he's had meetings with Steven's agent and I hope it's deal we can get done.
"No, we've not made no offers for really for anybody else. The boy [Christian] Poulsen from Ajax we've made contact with Ajax about him but that's dragged on a bit, I don't know where that's going to go.
"Jack Collison is here, whose been released and I'd like to help him if I can with his fitness and everything, he's a smashing boy."
One player set to leave Loftus Road is striker Loic Remy.
Having spent last season on loan at Newcastle United, scoring 14 goals in 26 league outings, the France international is reportedly in Liverpool's sights, but Redknapp insists contact is yet to be made from Mersyeside.
"I'm not sure what Loic [Remy] wants to do," Redknapp continued.
"He'll score goals, like I said before he went to Newcastle, he's a boy capable of getting 14-20 goals a year in the Premier League, no doubt, he's got the ability.
"He's a fantastic finisher and obviously we would like to keep him. But it's up to Loic, I'm not sure what he'd like to do.
"I think he'd really like to play Champions League football so that's what he's looking to do but if nothing comes along, I'm sure he'll come back here, give us everything he's got to make it a successful season here for him.
"[I've] never spoken to Liverpool about Loic, there's been nothing from them at all."
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