* Euro rises to one-week high versus dollar EUR=
* Ireland requests aid but peripheral worries remain
* Australian dollar buoyed by rising equity markets
(Changes lead, adds quote, detail, previous TOKYO)
By Neal Armstrong
LONDON, Nov 22 (Reuters) - The euro rose on Monday after Ireland sought an international bailout to tackle its debt crisis, but analysts said budgetary worries in other euro zone countries would keep investors wary about the single currency.
The euro climbed to a one-week high at $1.3786 EUR=, piercing the 38.2 percent retracement of its Nov 4-18 fall at $1.3765, with analysts saying a sustained break would be needed for a further correction towards resistance at $1.3864, a 50 percent retracement of that November sell-off.
Gains proved difficult to sustain, as the euro soon dropped back to trade at $1.3745, up around 0.4 percent on the day.
"The market is sceptical as there are still fiscal issues with Portugal and Spain. 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.
Foley said the reaction of peripheral bond yields would be crucial to near-term euro direction. Irish yield spreads over German benchmarks narrowed in early trade. [ID:LDE6AL0BW]
Data from the U.S. Commodity Futures Trading Commission showed on Friday highlighted uncertainty as speculators more than halved their euro/dollar long positions to 8,606 contracts last week from 23,283 contracts the week before. [ID:nN19210329] <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Ireland requests international bailout [ID:nLDE6AK0G8]
Europe debt problems [ID:nLDE68T0MG]
Euro zone debt struggle: r.reuters.com/hyb65p
Multimedia on euro zone crisis r.reuters.com/hus75h
The amount of European Union and the International Monetary Fund aid for Ireland has yet to be decided but is likely to be smaller than Greece's 110 billion euro bailout last May. A senior EU source said it could total 80 to 90 billion euros.
"Despite a shared currency, euro zone countries have various institutional differences, which investors may come to view as the fundamental problem of the currency," said Kimihiko Tomita, head of FX at State Street Global Markets.
Against the yen, the single currency rose 0.4 percent to 114.55 yen EURJPY=. Some Japanese exporters sold into the rally, but a sustained break above 115 yen and its Oct. 7 high around 115.68 could bring the euro out of its 112-115 range of the past two months.
The euro's rally helped drive the U.S. dollar index =USD .DXY to 78.66, down 0.4 percent on the day.
Dealers said trade was thin partly due to a Japanese market holiday on Tuesday and a U.S. market holiday on Thursday.
The greenback was a touch lower at 83.40 yen JPY=, though its surprise rebound this month from a 15-year low of 80.21 has kept many traders positive about it for the near term.
Considerable attention is on whether the dollar can rise sustainably above its daily Ichimoku cloud, now at 83.64.
The Australian dollar AUD=D4 was a standout performer, rising 0.8 percent to $0.9942, extending gains after having triggered stop-loss orders above $0.99.
The Aussie shrugged off further Chinese tightening measures announced on Friday and Asian and European stocks made steady gains.
Last Friday, China ordered lenders to lock up more of their money at the central bank for a second time in two weeks in a fresh attempt to keep a lid on inflation. [ID:nL3E6MJ0N8]
In contrast, the New Zealand dollar slipped after Standard & Poor's downgraded the outlook for its rating on the country's foreign currency debt, citing its widening trade deficit and credit risks in its banking sector. [ID:nSGE6AL05L]
The kiwi fell 0.9 percent against the U.S. dollar NZD=D4 to $0.7719 at one stage but recovered to stand around $0.7765 in European trade.
(Additional reporting by Hideyuki Sano)