Long had I believed both writings were OK. Long have I sworn my teacher in Japan said 'jitsu'. And even my business card says 'jitsu'. The window at my dojo says 'jitsu'. I was wrong.
from Jisho
術
art; means; technique - the kana for it's pronounciation is quite clear じゅつ = jutsu.
from romanjidesu
術
art; technique; skill; means; trick; resources; magic again in katakana - ジュツ = jutsu
from yamasa
術
again - ジュツ = jutsu
Jutsu - Wikipedia
Still refusing to believe? Let's look at some AikiJujutsu English language sites from Japan.
Jutsu - from daitoryu-roppokai
Jutsu - main line
Jutsu - from Kodokai
Jutsu - from hakkoryu
Last Chrismas I had the pleasure of sitting down with 20 Japanese teachers studying English at my wife's school. I asked them the jitsu versus jutsu question. They ALL told me it was jutsu. Still I refused to believe and pressed them further. They speculated that English speakers simply cannot easily pronounce jutsu so there was some pronounciation drift. Simply we like saying jitsu, just like Japanese people say 'wapuro' instead of word processor.