John fired off a letter to Paul days after an interview critical of him and The Beatles appeared in a November 1971 issue of British music magazine Melody Maker, and John's reply is mostly scathing ... but also thoughtful and pleading.

From the jump, John's frustration with Paul is clear ... telling Paul he's ungrateful for all the money he's getting from The Beatles. As the 3-page letter rambles on, John takes issue with Paul dismissing his song "Imagine" and berates Paul for being indecisive over the band's breakup.

The Beatles had been broken up for more than a year at that point, and were haggling over money. In the letter, John pleads with Paul to meet him without any lawyers ... then turns around and accuses Paul of buying up shares of another record company behind his back.

George Harrison and Ringo Starr also get roped in, as John rips Paul for telling the magazine George and Ringo would break him -- and also accuses Paul of threatening Ringo and his wife, Maureen.

The typed letter, which includes some of John's handwritten additions and signature, is being auctioned off by Gotta Have Rock and Roll ... and it's expected to fetch at least $30,000.

John also sent the letter to Melody Maker magazine editor Richard Williams, scribbling a plea for him to publish it ... and it appeared in the magazine a few weeks after Paul's interview ran.

There's also a fascinating postscript. John says he's puzzled Paul's interview mentioned leaving their wives, Linda and Yoko Ono, out of the dispute ... to which John replies, "I thought you'd have understood BY NOW, that I'm JOHNANDYOKO."