Coach Stu Jacobs predictably selected British-based players -- Celtic's Chris Killen, Fulham's Simon Elliot and Blackburn captain Ryan Nelsen -- in his 25-man squad.
However, he is keeping his options open with the inclusion of Lochhead and Smeltz.
Jacobs can field just three over-age players in the otherwise under-23 tournament, and plans to reduce the squad in July to a final list of 18, plus four non-travelling reserves, for the Games in Beijing in August.
"The experience of Ryan and Simon in the English premiership and Chris in the Scottish premiership is a huge bonus," Jacobs said.
"But we need to provide cover so we can still take our full quota if any of those five (including Smeltz and Lochhead) are unavailable."
The inclusion of the five over-age players boosts the number of All Whites in the squad to nine, with Jeremy Brockie, Daniel Ellensohn and former Phoenix pair Steven Old and Jacob Spoonley having already played key roles for the under-23 team during the Olympic qualifying tournament in Fiji in March.
Due to injury, non-selection and other commitments only Ellensohn, Killen, Lochhead and Smeltz have seen game time for the All Whites in recent World Cup qualifiers.
A dozen New Zealand Football Championship players have made the extended squad, with Hawke's Bay United contributing five and Waikato FC three.
Hawke's Bay United fullbacks Ian Hogg and Sam Jenkins, along with Sunderland's promising defender Jack Pelter -- who missed the Olympic qualifying due to an ankle injury -- are the only other new faces to the side.
But injury has dealt a cruel blow to United States-based Dan Keat.
The Dartmouth College midfielder who badly injured his knee in training for his Ivy League school, ending any chance he had to appear at the Olympics.
Jacobs had been awaiting results of an scan on Keat's injury before naming his squad.
He said Keat was "devastated".
"He's been a pretty consistent performer for the under-20s and the under-23s and now he's had that opportunity of playing on the Olympic stage taken away from him."
The New Zealanders face a high-profile Olympic debut against hosts China on the eve of the opening ceremony, followed by matches against Brazil and Belgium.
New Zealand extended squad:-
Goalkeepers: Liam Little (Otago Ut), Jacob Spoonley (unattached), Roy Bell (Macarthur Rams).
Defenders: Michael Boxall (University of Santa Barbara), Hone Fowler (Waikato FC), Ian Hogg (Hawke's Bay Utd), Sam Jenkins (Hawke's Bay Utd), Tony Lochhead (Wellington Phoenix), Joel Mathews (Auckland City), Ryan Nelsen (Blackburn Rovers), Steven Old (Macarthur Rams), Jack Pelter (Sunderland Athletic FC), Aaron Scott (Waikato FC).
Midfielders: Jeremy Brockie (Hawke's Bay Utd), Simon Elliott (Fulham FC), Craig Henderson (Dartmouth College), Cole Peverley (Hawke's Bay Utd), Cole Tinkler (Team Wellington), Shaun van Rooyen (Waikato FC).
Forwards: Costa Barbarouses (Wellington Phoenix), Greg Draper (Wellington Phoenix), Daniel Ellensohn (Team Wellington), Chris Killen (Glasgow Celtic), Sam Messam (Hawke's Bay Utd), Shane Smeltz (Wellington Phoenix).
