Sources with first-hand knowledge of the convo tell TMZ, Kanye called Trump to express his frustration over the Swedish judge's decision to hold A$AP Rocky for another week while the prosecutor decides whether to charge him ... even though we know that decision has already been made.

Kanye told Trump he wanted to get personally involved in the fight to free A$AP, and the first step was calling the President. Kanye discussed the fact Trump could call the Prime Minister ... and we're told Trump was agreeable.

The call was quick. We're told Kanye has a direct line into the Oval Office.

Trump said earlier, he's gotten a lot of calls from people in the African-American community over the A$AP situation ... but then said African-Americans and everyone else are one.

Trump said Melania also brought the A$AP matter to him, although we know Kim Kardashian called Jared Kushner about A$AP, who then went to Trump and Trump then contacted Pompeo.