* Euro falls vs dollar as Ireland aid fails to calm fears
* Peripheral European debt worries remain
* Technicals may pull euro toward a $1.31-$1.3350 range
* Moody's says multi-notch Ireland downgrade likely (Updates prices, adds detail)
By Steven C. Johnson
NEW YORK, Nov 22 (Reuters) - The euro slumped on Monday as worries about how a financial bailout for Ireland will be implemented doused investor optimism and failed to ease fears about other indebted euro zone countries.
The euro, which hit a one-week high near $1.38 overnight after the European Union and International Monetary Fund agreed to a rescue for Ireland, swiftly surrendered gains.
The currency at one point fell below $1.36 as the Irish government began to unravel, though it regained ground after Prime Minister Brian Cowen vowed to stay in office long enough to pass an austerity budget.
The euro was last down 0.4 percent at $1.3622.
Investors also feared the aid, which an EU source said could total 80 billion to 90 billion euros, may not be enough to backstop Irish banks or stop similar runs on assets in heavily indebted Portugal or Spain.
"The question is, 'What's next?'," said Matthew Strauss, an RBC Capital Markets strategist in Toronto. "It's hard to see how Ireland will get the economic growth needed to repay its debts, especially given the political uncertainty it faces. And given Portugal's finances, people wonder, 'Will it be next?'."
Portugal's debt burden is rooted in slow growth and an increasingly uncompetitive economy.
Overnight the euro rose as high as $1.3786 but analysts said a cluster of important technical levels between $1.3100 and $1.3350 could pull it into that range in the coming weeks.
The Aug. 6 intraday high of $1.3334 is the first significant support level, Strauss said, followed by $1.3211 and the 200-day moving average around $1.3139.
A solid break below those levels will probably be a tougher nut to crack, at least in the remaining weeks of 2010. "We would need new developments about Europe or a strong new reasons to buy the U.S. dollar," Strauss said.
The EU/IMF rescue will shore up a banking sector devastated by a housing collapse without Ireland having to borrow at extremely high rates on capital markets. Still, ratings agency Moody's said Monday a "multi-notch downgrade" on Ireland was now likely.
Irish Prime Minister Brian Cowen resisted calls for his resignation on Monday and vowed to stay in power long enough to pass an austerity budget.
EURO LONGS REDUCED
Data from the U.S. Commodity Futures Trading Commission on Friday highlighted uncertainty as speculators more than halved net euro/dollar long positions to 8,606 contracts last week from 23,283 the week before.and take profits for the year may also lift the dollar.
"Investors have been undecided on the euro for a while now and I can see that uncertainty lasting into year-end," said Jane Foley, senior currency strategist at Rabobank in London.
The euro also fell 0.6 percent at 113.45 yen. The dollar fell 0.2 percent to 83.26 yen. Its surprise rebound this month from a 15-year low of 80.21 has kept many traders positive in the near term.
Dealers said a Japanese holiday on Tuesday and a U.S. one on Thursday kept trading volume thinner than usual. (Additional reporting by Nick Olivari in New York and Jessica Mortimer in London; Editing by James Dalgleish)