* Euro steady on day, near 4-month high of $1.3890
* ECB's Trichet likely to keep hawkish tone and support euro
* Key resistance $1.3947/59, large option barriers $1.3950
(Adds quote, detail, updates prices)
By Neal Armstrong
LONDON, March 3 (Reuters) - The euro hovered near a four-month high and a key resistance area against the dollar on Thursday, supported by expectations that the European Central Bank is set to pave the way for rate rises later in the year.
Investors have pushed the euro up about 3 percent from a low hit on Feb. 14 on the view that ECB chief Jean-Claude Trichet, who speaks at 1330 after the bank ends a policy-setting meeting, will sharpen his anti-inflation rhetoric as oil prices continue to soar.
Some market players think the bank will switch three-month liquidity operations back to capped-limit, variable rate tenders -- a largely symbolic step in the phasing out of crisis support that could also help clear the way for a rate hike.
"Trichet should keep a hawkish tone today as data in the euro zone has continued to improve," said Manuel Oliveri, currency strategist at UBS in Zurich.
"Better manufacturing and labour market conditions, together with rising commodity prices, are increasing the risks of second round effects. This should keep the euro supported."
The euro was flat against the dollar at $1.3868
It was within sight of the 76.4 percent retracement of its fall from November to January at $1.3947, as well as its 200-week moving average at $1.3959. The euro has traded below the 200-week since mid-November.
Options traders reported Asian offers ahead of $1.3900 option barriers, with more significant option structures highlighted at $1.3950, said to be expiring March 10.
Some traders said there is a risk the euro could slip after the ECB meeting since many market players are already counting on the central bank to send strong signals that it will raise rates to counter inflation.
Data showed last week that speculators' long positions in the euro have soared to their highest since mid-October, pointing to the risk of profit-taking.
However accounts with a longer-term perspective, particularly those who rely on computer-generated trading signals, were being forced to buy the euro given its recent appreciation.
"Topside in euro/dollar is more painful to the medium-term market, and the system accounts will have to continue to buy," said a London-based spot trader.
OIL IMPACT
Market players said the currency's outlook in the longer term also hinges on where oil prices are going, as the dollar comes under pressure from rising oil prices.
Many investors believe that higher oil prices will push central banks to raise interest rates to combat inflation but that the Federal Reserve is likely to lag the ECB and others, maintaining broadly stimulative policy to support growth.
The dollar index was steady on the day at 76.691 <.DXY>, near a four-month low of 76.529 hit on Wednesday. Trendline support connecting its record trough and its 2010 low lies in the 76.15-25 area.
The U.S. currency also hit a one-month low of 81.57 yen on Wednesday, though thick bids around 81.50 yen were likely to limit further losses in the near-term.
The Swiss franc, traditionally sought in times of heightened geopolitical tension, slipped after an Al Jazeera report that Libya's Muammar Gaddafi and the president of the Arab League had agreed to a peace plan fronted by Venezuela's president, Hugo Chavez. [ID:nN02289530]
Arab League Secretary-General Amr Moussa later told Reuters the plan was "under consideration". [ID:nLDE72203U]
The dollar edged up 0.2 percent to 0.9253 franc