||You must approach the Levitical priests [and other members of] the supreme court that exists at the time. When you make inquiry, they will declare to you a legal decision.
Uvata el-hakohanim haLevi'im ve'el-hashofet asher yihyeh bayamim hahem vedarashta vehigidu lecha et devar hamishpat.
(Rashi; Ibn Ezra). Or, 'Levites [and] priests,' indicating that both should preferably be members of the supreme court (Sifri; Yad, Sanhedrin 2:2). Cf. 2 Chronicles 19:8. Or, 'the supreme court [associated with] the Levitical priests,' indicating that for the court to have full authority, the priesthood must also be functioning (Sanhedrin 52b; Yad, Sanhedrin 14:11). The priests were associated with the court because they were supported by the community (see Deuteronomy 18:1), and could therefore devote their entire time to Torah study (Abarbanel).
Or, literally, 'judge.' However, by tradition, this is speaking of the council of 70 elders, the first of which was appointed by Moses; cf. Numbers 11:16, 24 (Yad, Sanhedrin 1:3). Also see Exodus 24:1. In Talmudical times, this supreme court was known as the Sanhedrin. Besides being a court, this body also had legislative powers, see Deuteronomy 17:11.