They've both achieved international fame, both are extremely powerful, and both have their fair share of controversies -- but don't you DARE compare the Kardashian family to the Kennedys ... so says Robert F. Kennedy's daughter.

Kerry Kennedy -- a major human rights activist -- was out in D.C. yesterday when we asked how Kim K and the rest of the Kardashian squad could build a lasting family legacy like the Kennedys.

Kerry's response -- LAUGHTER ... followed by, "Are you comparing the Kennedys to the Kardashians?" ... followed by more laughter.

Sure, the Kardashians might be lacking in the accomplishment department, but they're also trailing when it comes to national scandals.

Kerry told us her family isn't worried about branding -- they just want to "serve" the American people.