Coach Fernando Santos has emphasised the importance of his older players ahead of Friday's first leg in Athens, and a sign of his faith in his experienced players is epitomised by his decision to recall striker Gekas, 33.
Gekas, who plays for Konyaspor in Turkey, has scored 24 goals in his 68 appearances for Greece while Karagounis, 36, has played 129 times and Katsouranis, 34, has 107 caps.
"I won't comment about any individual player, but we do have a lot of players who are under the threat of suspension, so we need give ourselves some options," Santos told reporters.
He added: "We have a lot of experienced players who will know how to win the first match without conceding a goal.
"The Romanians are an excellent team, but I believe we will be the ones to make it through."
Santos' team are in the playoffs after finishing behind Group G winners Bosnia on goal difference, while Romania were a distant second in their group behind the Netherlands and have not qualified for the World Cup since 1998.
With a playing style which makes them hard to beat but unspectacular up front, Greece chalked up an impressive record of eight wins in their 10 group matches, five of them by 1-0 scorelines.
That lack of goals cost them top spot but the omens seem to be on Santos' side ahead of the tie as the stern-faced Portuguese has a full-strength squad to choose from.
Celtic's George Samaras trained separately on Monday and Tuesday as a precaution to rest a troublesome knee but he is expected to be fit.
Gekas believes Greece's experience in seeing off Ukraine in the 2010 playoffs will stand them in good stead against Victor Piturca's Romania.
"It's a tough match for both teams but the good thing is that we have the experience of such games and I think if we are serious and disciplined we can get the result we want on Friday so we can go into the second leg full of confidence," he said.
Romania head into what forward Razvan Cocis characterised as the "biggest challenge of our careers", without injured captain Vlad Chiriches and with doubts hanging over goalkeeper Ciprian Tatarusanu, who is struggling with a back problem, but could be fit for the second leg in Bucharest.
Chiriches broke his nose during Tottenham Hotspur's defeat to Newcastle United in the Premier League on Sunday, with Dinamo Bucharest defender Dragos Grigore replacing him.
Manchester City goalkeeper Costel Pantilimon has also been drafted back into the squad after displacing England's Joe Hart from the Manchester City team, and Piturca will decide late who plays depending on Tatarusanu's progress.
Romania are aiming to end a 16-year absence from the finals.
"This is without doubt the most important and challenging tie of our careers," said Cocis.
"We really want to go to the World Cup and will fight with all our strength for it. We know Greece's style of play, they are a team that plays defensively and tries to wait for their opponents to make a mistake and capitalise.
"Our goal is to score in the first game, but even if we draw 0-0 it is a good result for us to take back home."
In a surprise move, Piturca has left out Ajaccio's Adrian Mutu, Romania's all-time joint leading scorer with 35 goals in 77 internationals.
"We don't have players of high quality, but they are very driven, skilful and, most of all, they have come together to form a strong group," Piturca said.
"It is a group I hope will grow exponentially to make its mark on both European and world football.
"It's extremely important that we qualify - for me as well as for the team, because I have managed to take the team through to three Euro finals but never to the World Cup.
"But it is even more important for the players, for whom playing in a World Cup would be an incredible experience and achievement."