(Recasts, adds details, quotes)
* Euro's gains run out of steam
* Geithner urges unity in tackling EZ crisis
* Juncker dashes expectations, leaves euro vulnerable
By Anirban Nag
LONDON, Sept 16 (Reuters) - The euro fell on Friday after euro zone finance ministers meeting in Poland gave no sign of fresh action to tackle the region's debt problems, following a call from U.S. Treasury Secretary Timothy Geithner for a united front against the crisis.
Geithner, whose presence at the meeting highlighted how concerned the United States is, said he believed Europe had the capacity to contain its sovereign debt crisis.
Some investors were expecting the ministers to announce concrete measures, with discussions focused on leveraging the euro zone's bailout fund to make it more effective.
But Eurogroup president Jean-Claude Juncker said the dialogue with Geithner was informal and they did not discuss increasing the size of the fund with a non-euro zone member.
The euro was last down 0.8 percent at $1.3764 , off a one-week peak of $1.3937 hit on Thursday but holding above a seven-month trough below $1.35 plumbed on Monday. The common currency has gained around 1.5 percent so far this week.
It fell to a session low of $1.3753 on the EBS trading platform, with traders saying it extended losses after stop-loss orders were triggered on the break of $1.3770, with more stops cited at $1.3750.
"All the headlines that are coming out of the Ecofin meeting are pretty negative and the euro's resilience after the coordinated action from central banks on Thursday seems to be coming off," said Jeremy Stretch head of currency strategy at CIBC World Markets.
"There were some who went into the meeting with high hopes and they appears at the risk of being dashed."
Technical charts indicated the euro would find support around $1.3745, the 23.6 percent retracement of the fall from $1.4548 on Aug.29 to $1.3495 on Sept.12.
The euro had hit a one-week high after a coordinated move by central banks on Thursday to provide dollars. Funding strains which had hit some euro zone banks, including large French ones, and were impacting the euro had appeared to be easing.
Wider spreads reflect elevated demand to borrow dollars in the currency forward market and often support the greenback's spot value against the euro.
In the options market euro/dollar month implied vols - measure of investor demand to protect against spot price volatility - were steady around 14.5 percent and off this week's high of around 18 percent .
One-month risk reversals in favour of euro puts -- a measure of the premium required to hold a put or a call in a currency --came in slightly at 2.5 from around 2.9.
FED EASING AHEAD
While investors are still wary of the euro, there was also reluctance to take long positions in the dollar ahead of a Federal Reserve meeting next week, where policymakers may flag further easing measures to boost the economy.
That move, dubbed QE3, would weigh on the greenback and help riskier assets rally, although analysts said some market players thought "Operation Twist" was more likely.
In such a scenario the Fed would buy longer dated Treasury bonds and sell the shorter dated ones to keep rates at the longer end lower without expanding the balance sheet.
"Most people are anticipating Operation Twist where you rebalance your balance sheet rather than expand it but there is some nervousness about QE3," said Daragh Maher, FX strategist at Credit Agricole.
"Twist would be positive for the dollar because it is stimulative to growth. It would be seen as delivering stimulus without printing a few extra billion dollars."
The dollar index was last up 0.5 percent at 76.623 . Against the yen, the dollar remained stuck at 76.69 yen . The threat of intervention from the Japanese authorities has helped keep the yen in a tight range and below its all-time high of 75.94 yen. (additiional reporting by Nia Williams; Editing by Toby Chopra, John Stonestreet)