* Global manufacturing and service activity steady in August
* U.S. Aug service sector PMI at highest since May
* Euro zone August composite PMI at four-year high
* Japan service sector expands at fastest in two years
* Services PMI momentum: link.reuters.com/vut72w
* European PMIs: link.reuters.com/suw32w
By Jonathan Cable and Clive McKeef
LONDON/NEW YORK, Sept 3 (Reuters) - Global manufacturing and service sector activity expanded in August at the same pace as in July, with both the U.S. and euro zone doing better than Asia, according to purchasing manager surveys.
"Scratching beneath the headline numbers, however, reveals an ongoing disparity between the relatively strong performance of the developed nations whereas growth in the emerging markets is quite weak," said David Hensley, a director at JPMorgan.
JPMorgan's Global All-Industry Output Index, produced with private data vendor Markit, held steady at July's 53.7 last month and has been above the 50 mark that divides growth from contraction since October 2012.
Markit's global service sector purchasing managers index (PMI) rose to 54.4 in August from 54.1 in July, though on Tuesday the world manufacturing PMI expanded at its weakest pace in just over two years last month.
"The trend in key regions such as Asia will need to improve if global growth in 2015 is to exceed its 2014 outcome," Hensley said.
The global PMIs combine survey data from countries including the United States, Japan, Germany, France, Britain, China and Russia.
In regional data, U.S. service sector growth in August reached its highest level since May, signaling good third-quarter economic growth.
Markit's final service sector PMI for August improved to 56.1 from 55.7 in July, but average prices charged by U.S. service businesses fell to end 25 straight months of increases.
"Inflationary pressures have abated, which will help the argument that interest rate hikes can be delayed," said Chris Williamson, Markit's chief economist.
An alternative survey from the U.S. Institute of Supply Management (ISM) also showed service sector growth remained robust during August but was off a 10-year peak reached in July. The ISM service sector PMI fell to 59 last month from 60.3 in July.
Elsewhere in the Americas, activity in Brazil's services sector fell for the sixth straight month in August, but contracted at a slower pace than in July, according to HSBC/Markit.
The more modest contraction, combined with a downturn in the manufacturing sector, lifted HSBC's Composite PMI to 44.8 in August from 40.8 in July, but nevertheless suggested Brazil's recession may have deepened in recent months.
"This bodes ill for the Brazilian economy, which will likely see further declines in activity in upcoming months," said Pollyanna De Lima, an economist with Markit.
Business activity in the euro zone accelerated at its fastest pace in more than four years in August, according to surveys that highlighted a divergence between laggard France and the other big economies in the currency bloc.
While generally upbeat, the set of surveys still point only to modest third-quarter economic growth growth of about 0.4 percent in July-September, according to Markit.
"The upwards momentum that the euro zone economy had has started to fizzle out, and growth no longer seems to be accelerating," said Nick Kounis, head of macro and markets research at ABN AMRO.
Markit's euro zone service sector PMI rose to 54.4 from July's 54.0, after the manufacturing PMI, released on Tuesday, dipped to 52.3 from 52.4.
Markit's final August Composite Purchasing Managers' Index (PMI) rose to 54.3, its highest level since May 2011. It has now been above 50 since July 2013.
Italian firms had their best performance since early 2011 and German growth strengthened. It was a different story in France, the bloc's second biggest economy, where the composite PMI slumped to its lowest since the start of the year.
On Thursday the European Central Bank cut its growth and inflation forecasts, warning of possible further trouble from China. At the same time, the euro zone central bank pledged to beef up or prolong its economic stimulus if needed, which helped global stock markets rally.
August was disappointing for the British economy too with the Markit/CIPS PMI for the service sector recording its weakest growth since May 2013, just as the Bank of England is considering when to start to raise interest rates.
"Let's face it, August was not a pretty month and a number of downside events will have weighed down on business sentiment and activity," said Kallum Pickering at Berenberg Bank.
Activity in Japan's services sector expanded at the fastest pace in almost two years in August, easing concerns about economic growth after disappointing industrial production and household spending data for July.
The Markit/Nikkei Japan Services PMI which rose to 53.7, the highest since October 2013, from 51.2 in July.
Japan's economy contracted in April-June as exports and consumer spending weakened. The government is counting on a return to growth in the current quarter to fulfil its pledge to revitalise the economy.
India's service sector grew for a second month in August, keeping pressure on the central bank for another rate cut to bolster a slowing economy. India's Nikkei/Markit services PMI rose to 51.8 in August from 50.8.
Economists remain concerned about China, where PMI data earlier this week from Ciaxin/Markit showed activity in both the manufacturing and service sectors slowing. Chinese stock markets, the source of much of the global volatility in recent weeks, were closed for a two-day holiday starting Thursday.
Additional reporting by Mike Connor in New York, Brad Haynes in Brazil, Aaradhana Ramesh in Bengaluru, and Stanley White in Tokyo; editing by Chizu Nomiyama