* Nasdaq bucks world trend and rises in off-market
* U.S. dollar rises as investors trim bearish bets
* Oil slides below $70 a barrel on signs demand still weak
* Long-dated bond prices slip ahead of Fed meeting (Updates with close of U.S. markets)
By Herbert Lash
NEW YORK, Sept 21 (Reuters) - The U.S. dollar rose on Monday, denting the price of commodities and raw materials stocks, as doubts about the sustainability of the rally in equities over the past few months unnerved investors.
The tech-rich Nasdaq rose, however, buoyed by a broker's upgrade on the biotechnology sector. But the Dow and broad S&P 500 index slipped, while MSCI's all-country world stock index <.MIWD00000PUS> was down 0.7 percent.
The dollar climbed against other major currencies, hitting a near two-week high against the yen, as investors trimmed big short positions ahead of this week's Federal Reserve monetary policy meeting and a summit of leaders from the Group of 20 major and developing nations. For details see [ID:nN21404300].
Oil prices fell more than 3 percent to under $70 a barrel on further signs of weak fuel demand, while gold fell to its lowest in almost a week, both pressured by a rallying dollar. [ID:nSYD151755] [ID:nLL670225]
"There are some thoughts in the markets that the (Federal Open Market Committee) might announce that they're going to start removing stimulus," said Chuck Butler, president of Everbank World Markets in St. Louis. "That's why the dollar is a little bit stronger."
The FOMC is widely expected to hold short-term benchmark U.S. interest rates unchanged near zero at the conclusion of its two-day meeting on Wednesday.
In the absence of key events or major economic data on Monday, traders took profits on currencies that have rallied against the U.S. currency, including the euro, which is up roughly 2.0 percent so far this month.
The dollar index <.DXY> rose 0.5 percent to 76.784 after three weeks of declines
The Dow Jones industrial average <.DJI> closed down 41.34 points, or 0.42 percent, to 9,778.86. The Standard & Poor's 500 Index <.SPX> slipped 3.64 points, or 0.34 percent, to 1,064.66. The Nasdaq Composite Index <.IXIC>, however, added 5.18 points, or 0.24 percent, to 2,138.04.
Energy <.GSPE> and materials <.GSPM> ranked as the S&P 500's worst-performing sectors, both down about 0.9 percent.
Copper rebounded from a 2-1/2-week low to end modestly higher after the dollar gave back some gains. Rising warehouse levels raised concerns about the near-term demand outlook. [ID:nLL546177]
"It's almost tracking the currencies one-for-one and there is very little else we can see," said Edward Meir, senior commodity analyst at MF Global. "The dollar is a short-term factor when there is not much else to hang their hat on."
Stock market losses kept a bid under safe-haven Treasuries, leaving short-dated securities in the plus column in late trade and longer-dated instruments with only narrow losses. [ID:nN21577578]
"Although equities are still down, we seem to be following the path of equities," said Mary Ann Hurley, vice president of fixed income trading at D.A. Davidson & Co in Seattle, adding "we do have a lot of supply to bid on this week."
Benchmark 10-year U.S. Treasury notes
The euro
European equity markets closed lower, with banks and miners retreating in particular, as some investors wondered whether the strong rally from March lows is close to conclusion.
Stocks that have led the recent recovery were hit hardest, with miners topping the list of decliners.
The pan-European FTSEurofirst 300 <.FTEU3> fell 0.7 percent to close at 999.06, the first time it closed below 1,000 since last Tuesday.
Trading was quiet as markets in Japan were shut until Thursday for holidays, while markets in India, Indonesia, Singapore, Malaysia and the Philippines were also shut.
U.S. crude for October delivery
Oil prices have more than doubled since hitting lows near $30 a barrel at the depths of the global economic crisis but the market has come under pressure since touching a year high of $75 a barrel almost a month ago.
Gold prices briefly dropped below $1,000 an ounce. Prices hit their weakest since Sept. 15 at $995.50, far from the 18-month high struck last week at $1,023.85.
The MSCI index of Asia Pacific stocks traded outside Japan <.MIAPJ0000PUS> dipped 0.6 percent, after surging 80 percent since mid-March when global markets started to rally on hopes that the financial crisis had bottomed out. (Reporting by Ryan Vlastelica, Gertrude Chavez-Dreyfuss and Chris Reese in New York and David Sheppard, David Brett and Simon Falush in London; Writing by Herbert Lash; Editing by James Dalgleish)