* Dollar rebounds from 2009 level
* Pound down after S&P cuts UK outlook, cites debt burden
* S&P action dampens risk appetite in markets (Adds comments, updates prices, changes byline, dateline, previous LONDON)
By Wanfeng Zhou
NEW YORK, May 21 (Reuters) - The U.S. dollar on Thursday rose from its lowest level so far this year on diminished investor risk appetite after Standard & Poor's said it could downgrade Britain's triple-A credit rating due to high debt.
Sterling dropped from a 6-1/2-month high against the dollar after the ratings agency revised its outlook on Britain to negative from stable, saying the country's debt burden would rise significantly. For more see [
].Analysts said the news reminded markets that the global economy still faces challenging times despite recent signs that the worst of the crisis may be past. That sentiment boosted safe-haven demand for the dollar and weighed on riskier assets such as equities and commodities.
"The most obvious one was the S&P action on the UK. That was like a wake-up call for the market overall," said Ronald Simpson, managing director of global currency analysis at Action Economics in Tampa, Florida.
"That action dented the risk appetite for now, so we've seen the dollar move marginally higher as a result," he added. "The market was getting a little ahead of itself. We still have some major issues to deal with."
In early New York trading, the ICE Futures dollar index <.DXY>, which tracks the greenback against a basket of six currencies, rebounded to trade up 0.2 percent at 81.329 after it plumbed its lowest level of the year at 80.799 earlier in the global session.
Recent optimism about a global recovery eroded safe-haven demand for the dollar, while minutes from the Federal Reserve's latest policy meeting showing the U.S. central bank had considered buying more securities added to pressure. [
]The euro fell 0.2 percent to $1.3741 <EUR=>, after rising to as high as $1.3837, according to Reuters data, its highest since early January.
The dollar <JPY=> traded slightly lower at 94.77 yen, but stayed in range of a two-month low of 94.28 yen hit on electronic trading platform EBS earlier in the day.
UK RATINGS
The pound tumbled as much as 3 cents against the dollar following the S&P's news, although it later trimmed losses as some in the market reckoned that Britain is only one of many nations facing deep fiscal problems.
Sterling <GBP=D4> traded at $1.5641, down 0.6 percent on the day, but pulled back from the day's trough of $1.5514 hit after the S&P announcement.
"The follow-through reaction is that the market has started to realize that if this is happening to the UK, who could be next?" said Paul Mackel, director of currency strategy at HSBC in London.
"If they're adjusting the UK's outlook because of fiscal concerns, certainly there are other candidates that would have to go down the same path."
Rival agency Moody's said its stable outlook for its UK Aaa rating is not under review, while Fitch said it had not changed its stable outlook and triple-A rating for Britain.
Analysts at ING in London said the United States may also be vulnerable, given that its debt-to-GDP ratio was worse than the UK's heading into the global financial crisis, and is expected to hit 100 percent before Britain's does.
"The market is right to ask whether a U.S. ratings outlook change could occur shortly -- which would be very bad news for the USD," they wrote in a research note. (Additional reporting by Naomi Tajitsu in London; Editing by James Dalgleish)