Leading media buyer ZenithOptimedia raised its 2010 global advertising growth forecast for the third time following a faster-than-expected recovery in the United States and Western Europe.

The agency, which is part of France's Publicis, now sees the market growing 3.5 percent, more than the 2.2 percent it predicted in April, with all regions expected to show at least some growth.

Most of the upgrade is in North America and in Western Europe (...) but these regions are still growing much more slowly than most developing markets, ZenithOptimedia said in a statement.

Developing markets are expected to drive most of the growth in global ad expenditure over the next few years, it added.

Developed markets would grow by 2.4 percent in 2011 and 2.9 percent in 2012, while developing markets were expected to grow by 9.1 percent and 9.8 percent respectively, propelled by the Asia-Pacific and Latin America regions.

ZenithOptimedia also raised its 2011 global ad spending forecast to 4.5 percent from 4.1 percent and confirmed its 5.3 percent growth expectation for 2012, up from a 2010 total of $448 billion and after a 10.3 percent drop in 2009.

The healthy third year after the downturn repeats the pattern of the last two recessions, though with lower growth this time, the agency said.

ZenithOptimedia now expects 2.2 percent growth in Western Europe this year despite concerns over euro zone debt, up from 0.4 percent before. Ad spending should increase gradually in 2011 and 2012, depending on demand as government austerity measures kick in later this year. The starkest contrast comes in North America, where the agency now forecast 1.3 percent growth in 2010 instead of a 1.5 percent decline, thanks to a strong recovery in consumer confidence and spending.

Television did relatively well in the downturn, when consumers tend to spend more time at home, and as new technologies such as hard-drive recorders encouraged them to watch even more TV.

Much more dominant in developing markets, TV is expected to attract 40.8 percent of the global ad market in 2012, up from 39.2 percent in 2009.

Internet ad spending, the biggest medium after TV and newspapers, should increase its share to 17.1 percent in 2012 from 12.7 percent in 2009, helped by very rapid growth in Internet mobile and social media, the agency said.

(Reporting by Cyril Altmeyer; Editing by Michael Shields)