Israeli army radio reported yesterday that Gabi Ashkenazi, a former general, will replace Dan Halutz as the chief of the Israeli army.  Halutz resigned last week after being heavily criticized for his role in the war in Lebanon last summer. According to Israeli Army Radio, Ashkenazi was appointed by the unpopular Prime Minister Ehud Olmert, and the defence minister Amir Peretz. The decision is yet to be approved by the Knesset.   Israeli media had predicted that Ashkenazi would get the job after his leading rival for the post, Moshe Kaplinsky, the deputy chief of staff, wrote a letter to Peretz dropping out of the race.   Ashkenazi's previous 'civilian' role as director-general of the defence ministry makes him a reasonably safe candidate to replace Halutz in advance of the preliminary findings of an inquiry examining the handling of the war in Lebanon.   Ashkenazi, 53, a retired major-general, fought in the 1973 Middle East War, and was also an officer in the first Lebanon war in 1982. He oversaw the withdrawal of all Israeli forces from south Lebanon in 2000.