The Dutchman sprang a minor surprise when he named both uncapped players in a 32-man squad earlier this month and they could win their first international caps against the Czech Republic in a friendly on June 1.
The 19-year-old Arzani plays can be deployed either in central midfield or on the wing, while Karacic, 22, plays at right back for club and country.
Socceroos all-time leading goalscorer Tim Cahill also retains his place as he looks to play in his fourth World Cup at the age of 38.
Van Marwijk’s side head to Turkey for a pre-tournament training camp after which the 65-year-old will announce his final 23-man World Cup squad before the FIFA deadline on June 4.
“I am sure that in training in Antalya, and in our match against the Czech Republic, we will see players pushing to go to a higher level as they compete for a place in the final squad,” he said in a statement.
Australia face France, Denmark and Peru in Group C at the June 14-July 15 finals.
Goalkeepers – Mat Ryan (Brighton and Hove Albion, England), Danny Vukovic (Genk, Belgium), Brad Jones (Feyenoord, Netherlands).
Defenders – Aziz Behich (Bursaspor, Turkey), Milos Degenek (Yokohama F. Marinos, Japan), Matthew Jurman (Suwon Bluewings, South Korea), James Meredith (Millwall, England), Josh Risdon (Western Sydney), Trent Sainsbury (Grasshoppers Zurich, Switzerland), Fran Karacic (NK Lokomotiva, Croatia).
Midfielders – Josh Brillante (Sydney FC), Mile Jedinak (Aston Villa, England), Jackson Irvine (Hull City, England), Robbie Kruse (Bochum, Germany), Massimo Luongo (Queens Park Rangers, England), Mark Milligan (Al Ahli, Saudi Arabia), Aaron Mooy (Huddersfield Town, England), Tom Rogic (Celtic, Scotland), James Troisi (Melbourne Victory).
Forwards – Tim Cahill (Millwall, England), Tomi Juric (FC Luzern, Switzerland), Matthew Leckie (Hertha Berlin, Germany), Andrew Nabbout (Urawa Red Diamonds, Japan), Nikita Rukavytsya (Maccabi Haifa, Israel), Dimitri Petratos (Newcastle Jets), Daniel Arzani (Melbourne City).
(Reporting by Simon Jennings in Bengaluru, editing by Ed Osmond)