OSLO, Nov 28 (Reuters) - The Norwegian sovereign wealth fund's proposed multi-billion dollar divestment from oil and gas stocks will take many years to complete, Chief Executive Yngve Slyngstad told reporters on Tuesday.

The $1 trillion fund, the world's largest of its kind, proposed on Nov. 17 to drop oil and gas stock from its index, but needs approval from Norwegian authorities to do so.

(Reporting by Gwladys Fouche, editing by Terje Solsvik)