UPDATE 1-Chrysler loan payoff could save it $300 mln/yr-CEO

* Chrysler plans to pay off US govt loans on Tuesday * Payoff will raise Fiat's stake in Chrysler to 46 pct * Marchionne sees Fiat stake rising to 76 pct "over time" (Adds quotes, background) By Ben Klayman MACOMB, Mich., May 23 (Reuters) -...