* Euro falls to $1.3345 <EUR=>, 10-month low
* Fitch Ratings cuts Portugal's sovereign rating
* Dollar index <.DXY> hits highest since May 2009
* Swiss franc climbs to record high vs euro (Releads, adds quote, updates prices)
By Tamawa Desai
LONDON, March 24 (Reuters) - The euro fell to 10-month lows against the dollar on Wednesday as a ratings firm downgraded Portugal's debt and on speculation little of substance to aid debt-laden Greece would emerge in coming days.
Fitch Ratings lowered Portugal's sovereign credit rating to AA- from AA, with a negative outlook. [ID:nWLB0770]
An already weak euro fell to the day's low of $1.3345 <EUR=>, down 1.1 percent and its lowest since early May 2009. By 1102 GMT, it was down 1.0 percent at $1.3360.
Traders said a raft of stop-losses had been hit through the previous 2010 low in the $1.3440/30 area in Asia, with option-related stops then hit through $1.3400/1.3390 in Europe.
"The euro is independently weak, with a significantly better-than-expected reading on the German Ifo proving only a temporary distraction from the problems in the periphery," said Adam Cole, global head of FX strategy at RBC Capital Markets.
The German Ifo institute's business climate index rose to 98.1 from 95.2 in February, far higher than forecasts for 95.8. [ID:nLDE62N0R4] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
For a graphic comparing Ifo and German PMIs, click
The market will keep a close eye on an EU summit on Thursday and Friday, after Germany signalled for the first time that it may accept European financial aid for Greece as a last resort.
But Germany pegged its support to several conditions, including the need for the International Monetary Fund to make a "substantial contribution". [ID:nLDE62M130]
"The uncertainty over an aid package for Greece is clouding judgment towards the euro. Even if the IMF comes in, it shows the EU is not able to help itself," said Antje Praefcke, currency strategist at Commerzbank.
Investors flocked to the perceived safety of the U.S. currency, pushing the dollar to its highest since May last year against a basket of currencies.
The dollar index, which tracks the performance of the greenback versus six other major currencies, was up 0.8 percent at 81.578 <.DXY> after a 10-month high of 81.632.
The greenback rose to a one-month high against the yen at 91.29 yen <JPY=> while it hit a two-week peak against the Swiss franc at 1.0701 <CHF=>, according to Reuters data.
Higher risk currencies such as the Australian and New Zealand dollars also fell 0.7 percent against the U.S. dollar.
Traders also cited a shortage of dollar supply in the money markets as the end of the financial quarter approached, together with a potential liquidity squeeze over the Easter break.
Sterling slipped back below the $1.5000 level <GBP=D4> as the market awaited UK finance minister Alistair Darling's budget due at 1230 GMT.
Also in focus was the Norwegian central bank's latest decision on interest rates at 1300 GMT. Consensus is for no change, though some see risks of a 25 basis point increase.
Meanwhile, the euro traded flat versus the Swiss franc at 1.4280 francs <EURCHF=>, after hitting record lows to $1.4232 on trading platform EBS in Asia.
Swiss National Bank President Phillip Hildebrand said on Tuesday the central bank would keep fighting excessive franc appreciation. But traders expect it to shy away from large-scale intervention as the economy recovers. [ID:nLDE62M0D9]
Technical analysts said there was little to support the euro on the charts against the franc, ahead of a 32-year support line which came in at 1.4205 francs.
(Additional reporting by Neal Armstrong; graphic by Scott Barber; editing by Nigel Stephenson)