SYDNEY, Jan 20 (Reuters) - Australian shares are set to open lower on Wednesday, losing nearly half the gains achieved in the previous session. The local share price index futures eased 0.3 percent to 4,829.0, a 74-point discount to the underlying S&P/ASX 200 index .AXJO. The benchmark rose 0.74 percent on Tuesday, a day after hitting a 2-1/2 year closing low. New Zealand's benchmark S&P/NZX 50 index was little changed in early trade. For a summary of overnight action across global