The Yankees' greatest ally to keeping Hiroki Kuroda might be the righty's desire to play in Japan again while he still is a good pitcher. That is because, The Post has learned, the Yankees are only willing to offer Kuroda a one-year contract at present. Two other teams that seemingly would be attractive to Kuroda, the Dodgers and Angels, probably would be willing to offer at least a two-year pact. Japan also is a legitimate consideration for Kuroda right now. But if he decides he wants to pitch in the States further, he might be attracted to a one-year contract so he does not grow ineffective during the life of the deal and return to Japan unable to pitch at a high level. That would assist the Yankees, who only want to go one year, but badly need Kuroda to strengthen the top of their rotation. The Yankees do not want to go more than one year with Kuroda for two reasons: 1) They remain determined to get under the $189 million luxury tax threshold in 2014, so they are hesitant to add dollars beyond 2013. 2) They are comfortable giving older players one-year contracts so if they falter they are not committed beyond just that season. Kuroda turns 38 in February, and as well as he pitched in 2012 — he was the Yankees' most consistently good/durable starter throughout the year — the organization is concerned about how long he will sustain that excellence.