UPDATE 1-ITV ad revenue seen up 4 percent in December

* Oct NAR down 3 pct, Nov down 1 pct, Dec up 4 pct * 9-month revenue 1.31 bln stg vs 1.47 bln stg

* Extends lead over BBC1 in peak time viewing

(Adds details)

LONDON, Nov 5 (Reuters) - ITV (ITV.L), Britain's biggest commercial free-to-air broadcaster, said its net advertising revenues (NAR) are expected to rise 4 percent in December, with NAR flat for the quarter.

"Whilst our visibility is limited, the outlook for the fourth quarter has continued to improve and ITV is continuing to outperform the market," said chief operating officer John Cresswell.

Over the full year, total UK NAR is forecast to be down 12 percent.

The broadcaster, which is still struggling to find a new chairman and chief executive, said cost savings were on track with ITV set to deliver 155 million pound of savings in 2009.

(Reporting by Julie Crust; editing by Matt Scuffham)