UPDATE 1-Glaxo wins U.S. approval for swine flu vaccine

* FDA approves unadjuvanted H1N1 pandemic vaccine

* Glaxo plans to ship all 7.6 mln doses in December

* Vaccine will contribute small amount to U.S. needs (Adds details, background)

NEW YORK, Nov 10 (Reuters) - GlaxoSmithKline Plc (GSK.L) has won U.S. marketing approval to sell an unadjuvanted H1N1 swine vaccine, allowing it to ship relatively modest amounts of scarce vaccine to the United States next month.

The British company said on Tuesday the Food and Drug Administration had approved a modified version of its FluLaval seasonal flu vaccine containing the new H1N1 strain.

The green light clears the way for it to fill a order for 7.6 million doses from the U.S. government.

Glaxo is one of the world's largest manufacturers of flu vaccines, along with Sanofi-Aventis SA (SASY.PA) and Novartis AG (NOVN.VX).

But it is not a big source of swine flu vaccine for the United States, since its main H1N1 vaccine Pandemrix contains an adjuvant, or additive, and is not being used here.

The company's chief executive, Andrew Witty, told reporters last month that it would be only a "bit-part player in the U.S. flu scenario."