UPDATE 2-Japan FX intervention totalled $25.4 bln in Sept

* Aug. 30 - Sept. 28 intervention was 2.12 trln yen

* Japan resumed yen-selling intervention on Sept. 15

* Data suggest Japan intervened only on that day - analyst

(Adds more comments)

By Masayuki Kitano

TOKYO, Sept 30 (Reuters) - Japanese authorities spent 2.1249 trillion yen ($25.37 billion) on currency intervention in the month to Sept. 28, the Ministry of Finance said on Thursday.

That amount was roughly in line with market estimates of about 2 trillion for Sept. 15 alone, the only confirmed instance of Japanese currency intervention during that period.

"This suggests ... that there was only intervention on Sept. 15," said Masafumi Yamamoto, chief FX strategist Japan at Barclays Capital.

"It was very effective but unfortunately afterwards the Fed changed its rhetoric about quantitative easing and that's why the effect of the intervention was mitigated."

Finance Minister Yoshihiko Noda confirmed that Tokyo had made its first foreign exchange intervention in six years on Sept. 15, when the dollar hit a 15-year low of 82.87 yen JPY=.

The dollar also spiked last Friday on rumours of further intervention, but there was no confirmation and the dollar lost all its gains by the end of the day. Money market data later showed it was unlikely and Prime Minister Naoto Kan also said that day he was unaware of any new intervention.

Analysts said they still wanted to see the daily breakdown due in November to be sure.

Junya Tanase, chief FX strategist for JPMorgan Chase Bank in Tokyo, said whether or not there was intervention last Friday was not a vital issue.

"In either case, there will be no change to our view that this bout of intervention will likely end after a short while and with a small amount," Tanase said.

Although G7 officials so far have not complained loudly about Japan trying to stem the yen's strength, some market players harbour doubts about how aggressively Japan may be able to intervene.

Attempts to cheapen the yen could run counter to U.S. President Barack Obama's plan to double U.S. exports, and might also contrast too starkly with China's recent move to allow its currency to rise against the dollar.

Brazilian Finance Minister Guido Mantega said this week the world is in an "international currency war" as governments manipulate their currencies to improve their export competitiveness. [ID:nN27256208]

If confirmed that the intervention for the month all took place on Sept. 15, that will beat the previous record of 1.666 trillion yen for Japanese yen-selling intervention on a single day, set on Jan. 9, 2004.

The MOF will announce details such as specific intervention dates and currency breakdowns when it unveils its July-September intervention data, expected in early November.

The dollar has been under selling pressure on speculation the Federal Reserve will take more quantitative easing steps later this year to shore up the U.S. economy.

That has driven the yen higher, which has acted as a drag on Japanese exports and raised concerns in Tokyo that it could derail a fragile economic recovery and exacerbate deflation.

"With regard to future intervention, I think what will drive them is whether dollar/yen equals its 15-year lows or breaks below that level," said Ian Stannard, senior currency strategist at BNP Paribas in London.

The dollar was trading near 83.30 yen JPY= on Thursday, less than half a yen above its 15-year low. It leapt 3 yen on Sept. 15 to 85.78, when the authorities intervened throughout the Asian, European and U.S. trading day.

The Bank of Japan intervenes on behalf of the Ministry of Finance and traders said Sept. 15 was also probably the first time it had conducted intervention by directly placing orders on electronic trading platform EBS.

Before then, Japan had not intervened in the foreign exchange market since March 2004, when it ended a 15-month, 35 trillion yen selling spree aimed at preventing a strong yen from snuffing out an economic recovery.

(Additional reporting by Charlotte Cooper and the London forex team; Editing by John Stonestreet)