Former Wales captain Howley will take charge of next month's Millennium Stadium clash against the Barbarians and three-Test Australia tour while Gatland recovers from fractures to both heels sustained after a fall at his holiday home in New Zealand last month.
Gatland has led Wales to a World Cup semi-final and two title, Grand Slam-winning RBS 6 Nations campaigns since taking over as national coach in early 2008.
"The influence Warren has had on my coaching career is huge," said Howley, who today named four uncapped players among a 38-man training squad for the Baa-baas clash and Australia trip.
"He has been a huge mentor to me. It's immeasurable, really. I wouldn't be sat here if it wasn't for Warren.
"When you look at his CV and the trophies he has won, it speaks for itself. His biggest strength is he is straight down the line - he is honest."
Howley has been in regular contact with 2013 British and Irish Lions coaching favourite Gatland, who is recuperating at home in Hamilton following the fall.
"It is nice to catch up and see how he is convalescing," Howley added.
"It's great to have someone you can talk to, whether it is on life or rugby.
"He has got his sense of humour back. He saw a surgeon last week and he is on track that things are progressing nicely."
Howley's current group of players will be reduced to 34 for the mission Down Under, but one headline selection to face the Barbarians will be flanker Martyn Williams, who is poised for his 100th cap.
Howley, meanwhile, confirmed that locks Ian Evans and Alun-Wyn Jones will both miss the first Test in Brisbane on June 9. Evans is getting married, while Jones is attending his sister's wedding.
And that should herald a recall for Bradley Davies, who was cited following a dangerous tackle in Wales' opening Six Nations game against Ireland and then missed the tournament remainder through suspension.
A 15-strong Test group will head to Australia two days before the Barbarians fixture, led by defence coach Shaun Edwards, with the remaining players flying out on June 3, Evans apart, who will set off after his wedding.
The four Test rookies named are Scarlets full-back Liam Williams and prop Rhodri Jones, 19-year-old Cardiff Blues wing Harry Robinson and Ospreys centre Ashley Beck.
Injuries mean that centre Jamie Roberts and hooker Huw Bennett are unavailable, while, as expected, there is no place for controversial former Blues and Ospreys back Gavin Henson.
The squad will officially assemble next Monday, with the exception of a sizeable Ospreys contingent that will be preparing for the RaboDirect PRO12 final against Leinster six days later.
"The Ospreys will have our full backing in their bid for silverware in a fortnight's time, so we will not be asking them to join us until a week after everyone else," Howley said.
"We hope to get the summer off to a winning start against the Barbarians, and everyone who figures in that game will be playing for a place on the tour."
France-based Mike Phillips and James Hook will be with the squad from the start of its preparations, while skipper Sam Warburton remains firmly on course to recover in time from a shoulder injury.
But Clermont Auvergne full-back Lee Byrne has not been selected as he is still likely to be involved in France's domestic competition title race, although he will remain on stand-by.
"The litmus test is the challenge in the southern hemisphere. Coming off a Grand Slam win, we have got a great opportunity in the summer," Howley said.
"It is a huge challenge to play three Tests in any southern hemisphere country. Playing against Australia is going to be a huge test for us, but one that we are looking forward to. We are in good shape.
"While we have achieved Triple Crowns and Grand Slams, you can only look at the record books and history to see how many times a national side has beaten a major southern hemisphere team away from home.
"It would be a great achievement to win against a southern hemisphere team away from home, whether that is Australia, South Africa or New Zealand.
"If you are going to talk about being involved in World Cup semi-finals and finals, I think winning in the southern hemisphere is something that should be on your agenda.
"England showed the way when they did it in 2003 when they beat Australia and New Zealand away from home. It's a good test of where you are as a team."
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