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By Anirban Nag

LONDON, Sept 10 (Reuters) - The dollar gave up most of itsgains versus the yen on Friday, heading towards 15-year lows andkeeping intervention prospects alive, while the euro ralliedagainst the Swiss franc as investors sold safe-haven currencies.

Chinese trade data which showed higher-than-expected importsfor August along with news that Dubai World had reached a deal torestructure liabilities boosted risk demand and pushedcurrencies such as the Australian dollar higher.

The dollar fell against a basket of currencies, havingfailed to hold above the index's 55-day moving average at 82.80.Against the yen, the dollar was off its session highs of 84.28yen, falling to 83.90 yen.

It rose earlier in the session, helped by an increase inU.S. Treasury yields on Thursday on U.S. jobs data.

"There has been a moderate improvement in risk appetitewhich is seeing the dollar fall," said Daragh Maher, deputy headof global foreign exchange research at Credit Agricole CIB. "Butit is still very quiet there and its unlikely to lead to anytrend."

The euro was up 0.25 percent at $1.2727, helped mostly byits gains against the Swiss franc.

It rallied more than 1 percent against the franc, which cameunder selling pressure due to the rise in risk appetite. Theeuro hit the day's high of 1.3050 francs, according to Reutersdata. Traders cited Swiss banks selling the safe-haven francagainst the euro, dollar and other currencies.

But strategists remained sceptical about the euro's gains,given the euro zone periphery's debt worries and banking sectorproblems surfacing again.

"It is a risk-on environment which is helping the euro, butclearly structural problems remain given widening spreads andwell known problems about its banking sector," said SimonDerrick, head of currency research at Bank of New York Mellon.

His bank's data showed demand was not recovering for marketslike Greece, Italy and Portugal.

LEADERSHIP RACE TO SWAY YEN

The shift away from safe-haven currencies also kept the yenunder pressure against the higher-yielding currencies and theeuro. But the yen managed to pare some of its losses against thedollar as Japanese authorities kept up their rhetoric aboutintervention in the currency market.

The dollar hit a 15-year low of 83.34 yen this week,intensifying speculation that Japan might step in to curb yengains if the move accelerated towards 80 yen. Prime MinisterNaoto Kan reiterated on Friday that authorities would takedecisive steps on the yen if needed.

Attention was turning to a ruling party leadership race onSept. 14 in which Kan faces a challenge from powerbroker IchiroOzawa.

A Reuters poll showed a win by Ozawa in the vote, whichwould also decide who is prime minister, would likely give ashort-term boost to stocks but weaken Japanese government bondsand the yen.

Ozawa has said Japan should intervene to weaken the yen, andwhile some analysts say intervention would be difficult withoutsupport from Washington, others say Tokyo under Ozawa would bemore likely to take action if the yen strengthens.

"So the chances of intervention will rise as compared to theperiod under Kan," said Masafumi Yamamoto, chief FX strategistJapan at Barclays Capital in Tokyo.

(Additional reporting by Hideyuki Sano in Tokyo)