Gatland is poised to name Ireland captain Rory Best, Owens and Jamie George, Hartley's deputy in Jones's squad, as the three hookers in the squad that will be announced at midday today.
Hartley's omission is expected to be just one of a number of standout decisions, with Harlequins centre Jamie Roberts, a veteran of the 2009 and 2013 tours, expected to earn a surprise inclusion despite losing his place in the Wales starting XV during the Six Nations campaign.
Jack Nowell, the Exeter wing, has also made the cut despite failing to secure a regular starting place for England this season, while Leigh Halfpenny, the Wales full-back who was the place-kicking hero of the 2013 tour, is also expected to be in the squad despite his indifferent form for his country.
Gatland is likely name up to 40 players, just four fewer than Sir Clive Woodward took to New Zealand on the ill-fated 2005 trip.
Injury concerns over Sam Warburton, the Wales flanker who will be named as captain for the second successive tour, the first since Martin Johnson, in 1997 in South Africa and Australia in 2001, to do so, and Alun Wyn Jones, the Ospreys lock, are expected to mean that Gatland will also name Ireland locks Iain Henderson and Donnacha Ryan.
Scotland's disappointing finish to their Six Nations campaign after a hugely promising start, however, is expected to mean that Vern Cotter's side will contribute just one player, full-back Stuart Hogg.
England, despite the detrimental impact of their defeat by Ireland in Dublin, are still expected to provide the largest contingent of players of the four home unions, with 15 likely to be named in Gatland's squad, including rookies Kyle Sinckler, the Harlequins prop, and Ben Te'o, the Worcester centre.
The Daily Telegraph revealed yesterday that as well as Hartley, five other starters from England's Six Nations-winning side would miss out: George Ford, Jonathan Joseph, Mike Brown, Joe Launchbury and James Haskell. Chris Robshaw, who sat out the Six Nations with a shoulder injury but is now fit again, will also not be picked.
But while Hartley will miss out, George will be included, and England will also provide the bulk of the front five, with Joe Marler, Mako Vunipola and Dan Cole ajoining Sinckler among the six props, along with Ireland's duo Jack McGrath and Tadhg Furlong. George Kruis, Maro Itoje and Courtney Lawes will be named along the locks.
The back row, which has been the most ferociously competitive area of all, is expected to be dominated by Ireland and Wales, with Sean O'Brien, Peter O'Mahony, CJ Stander, Warburton and Justin Tipuric making up the flankers.
Billy Vunipola, of Saracens and England, and his Wales counterpart Taulupe Faletau, will be the two No 8s.
There are expected to be few surprises at fly-half, with Ireland's Jonathan Sexton in pole position for the starting place in the Test side, and Wales's Dan Biggar also making the cut.
The centre position is one of the more intriguing aspects of the selection. Definitely in are England's Owen Farrell, who will also cover fly-half, Ben Te'o and Elliot Daly.
Roberts, who started for Wales against Australia and Japan in the autumn Tests but who has been restricted for six appearances from the bench since then, is destined for a surprise call-up along with compatriot Jonathan Davies and Ireland's Robbie Henshaw.
Halfpenny, despite an underwhelming Six Nations campaign, is a loyal lieutenant of Gatland and he will be joined in the back three positions by Hogg, Welsh pair George North and Liam Williams, England's Anthony Watson and Nowell, and possibly Irish wing Keith Earls.
"It will be the strongest Lions squad ever to leave these shores," Lions tour manager John Spencer told The Telegraph.
"It has been a difficult process. You have to consider whether the player is world class. You have to consider whether he would be a good tourist in other personality aspects. The considerations that I have experienced have been extremely fair and thorough and very detailed. I absolutely and fundamentally believe we can win the series. That is our sole objective at this stage and we are not contemplating any other alternative."
The Lions squad as expected by the Telegraph
Back three: Stuart Hogg (Scotland), Leigh Halfpenny (Wales), George North (Wales), Jack Nowell (England), Anthony Watson (England), Liam Williams (Wales), Keith Earls (Ireland)
Centres: Elliot Daly (England), Robbie Henshaw (Ireland), Ben Te'o (England), Jonathan Davies (Wales), Jamie Roberts (Wales)
First-five: Johnny Sexton (Ireland), Owen Farrell (England), Dan Biggar (Wales)
Halfbacks: Conor Murray (Ireland), Ben Youngs (England), Rhys Webb (Wales)
Props: Joe Marler (England), Mako Vunipola (England), Jack McGrath (Ireland), Tadhg Furlong (Ireland), Kyle Sinckler (England), Dan Cole (England)
Hookers: Rory Best (Ireland), Ken Owens (Wales), Jamie George (England)
Locks: Maro Itoje (England), George Kruis (England), Courtney Lawes (England), Alun Wyn Jones (Wales), Donnacha Ryan (Ireland), Iain Henderson (Ireland)
Flankers: Sean O'Brien (Ireland), Peter O'Mahony (Ireland), CJ Stander (Ireland), Sam Warburton (Wales), Justin Tipuric (Wales)
No 8: Billy Vunipola (England), Taulupe Faletau (Wales)
