Windsor Park hosts the first leg on Thursday, with the return in Basel on Sunday and a place in next year's tournament in Russia at stake.
Northern Ireland are aiming to reach a World Cup finals for the first time since 1986 and secure a place at consecutive major tournaments for the first time in their history.
"We need it to be close because I don't think we are going to come through a high-scoring tie," O'Neill told BBC Sport.
"It's important not to concede at home. We are not a team suited to going out and chasing the game.
"We want to have something to take to Basel with us. The games will be tight and close and we can hopefully go there and play on the counter-attack with something to defend."
Northern Ireland competed at Euro 2016, reaching the second round of the tournament.