JAKARTA, Aug 2 (Reuters) - Indonesia's economy grew at its slowest rate for almost three years in the second quarter, adding to concerns that one of Asia's most vibrant economies is losing some of its steam.

The statistics bureau announced on Friday that GDP growth in the April-June period was 5.81 percent, its lowest since the third quarter of 2010 and below a Reuters poll of economists, which predicted a 5.95 rise from a year earlier.

The latest quarter was the fourth straight in which the growth pace slipped.

It adds to a string of discomforting data, including inflation running at a 4-1/2 year high, persistent trade and current account deficits and a slump in the rupiah, which has slid 6.3 percent this year to become emerging Asia's second worst performing currency after the Indian rupee.

The declining growth pace shows the economy is moderating, 'clearly signalling the drag created by the weakening of the rupiah, which we think has affected investment growth,' said OCBC economist Gundy Cahyadi.

Fixed capital formation increased an 4.7 percent in the latest quarter from a year earlier, compared with 5.9 percent in January-March.

In the first quarter, Southeast Asia's largest economy had annual growth of 6.02 percent.

A TRIMMED FORECAST

The government is targetting 6.3 percent this year, but the central bank last month trimmed its own forecast to 5.8-6.2 percent from 6.2-6.6 percent.

Compared with the first three months of 2013, GDP growth in April-June was 2.61 percent, also below predictions by economists of a seasonally-unadjusted expansion of 2.75 percent.

Exports continue to drop as major markets slow and prices decline for commodities - the mainstay of Indonesia's trade with the outside world.

Meanwhile, inflation has become a major headache, due to a sharp hike in fuel prices from June and surging costs for some basic foods.

'It seems to us that not only is economic growth softening more sharply than the official numbers suggest, but the consensus will continue to be surprised on the downside in coming quarters,' said Robert Prior-Wandesforde, Credit Suisse Asia economist.

'This bodes badly for the rupiah, unless the current account deficit improves much more than we expect it to do, while we suspect the earnings expectations of equity analysts are generally too high in economically sensitive sectors,' he wrote.

Credit Suisse forecasts Indonesian growth at 5.7 percent this year and 5.3 percent in 2014.

Bank Indonesia, the central bank, said on Thursday that it expects inflation and the current account deficit to start receding later in the year.

On Thursday, the statistics bureau said annual inflation in July was 8.61 percent.

(Reporting by Nilufar Rizki and Adriana Nina Kusuma; Writing by Jonathan Thatcher; Editing by Richard Borsuk) Keywords: INDONESIA ECONOMY/GDP

(rieka.rahadiana@thomsonreuters.com)(+6221 3199 7170)(Reuters Messaging: rieka.rahadiana.thomsonreuters.com@reuters.net)

COPYRIGHT

Copyright Thomson Reuters 2013. All rights reserved.

The copying, republication or redistribution of Reuters News Content, including by framing or similar means, is expressly prohibited without the prior written consent of Thomson Reuters.