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Ariana Grande straight-up ripped off the lyrics and melody to "7 Rings" -- so claims a songwriter who says he recorded basically the same song 2 years earlier.

Josh Stone claims in a new lawsuit -- obtained by TMZ -- he wrote a song called "You Need It, I Got It" in January 2017 ... 2 years BEFORE Ariana recorded "7 Rings."

Stone -- who goes by Dot -- notes in his suit, the hook to Ariana's song is, "I want it, I got it, I want it, I got it." His hook is, "You need it, I got it. You want it, I got it."

He also says the 2 songs have identical metrical placement of the paired phrases.

Stone says he took meetings with music industry execs and producers, including honchos from Universal Music Group ... the same company that published "7 Rings." Stone says he had a meeting in 2017 with Tommy Brown, who worked with Ariana on each of her 5 studio albums. Stone says Brown was interested in the song and said he liked it a lot.

Stone wants profits from "7 Rings" and an order from a judge prohibiting "7 Rings" from seeing daylight.