* MSCI Asia ex-Japan falls to near two-week low, materials lead decline
* End-month, end-quarter, Japan fiscal first-half adjustments set flows
* Yen near one-week high vs dollar, bids seen at 77.50 yen
* Euro falls to two-week lows vs yen, dollar
* European shares likely to decline
By Chikako Mogi
TOKYO, Sept 26 (Reuters) - Asian shares and commodities fell on Wednesday as investors turned their back on perceived stimulus effects from central bank easing, focusing instead on Europe's fiscal challenges as Spain faces bitter protests against budget austerity measures.
Flat U.S. stock futures hinted at a steady Wall Street open, but financial spreadbetters expected London's FTSE 100, Paris's CAC-40 and Frankfurt's DAX to open down as much as 1 percent.
"Despite ample liquidity in the market, investors remain concerned about whether economic fundamentals are really improving," said Kim Hak-kyun, an analyst at Daewoo Securities.
Flows were also driven by accounting calendar adjustments, with this weekend seeing the month-end, the end of the July-September quarter, and in Japan, the fiscal first half.
The MSCI index of Asia-Pacific shares outside Japan slid 1 percent to its lowest since Sept. 14, giving back nearly all the gains made after markets across riskier asset classes cheered the U.S. Federal Reserve's aggressive new job-boosting stimulus.
The European Central Bank said earlier this month it would buy the bonds of struggling euro zone states if they requested aid, while the Bank of Japan followed the Fed's example by increasing bond buying to help support the economy.
But market rallies have quickly been overtaken by concerns about deteriorating world economies.
"The markets are feeling, as if they didn't know before, that the magic of central bank stimulus is only to boost sentiment - not to fix fundamentals," a financial markets expert told Reuters.
The MSCI index's materials sector led the declines with a 1.8 percent drop. U.S. crude fell 0.6 percent to $90.79 a barrel and Brent eased 0.6 percent to $109.83. London copper shed 0.9 percent to $8,204 a tonne.
Australian shares fell 0.3 percent, as concerns over the global economic recovery dampened China's demand for industrial metals, a major export sector for Australia.
"The reason that these (stimulus) packages have to be pursued is because the underlying level of industrial production and economic growth is very weak," said Ben Lyons, an investment analyst at ATI Asset Management.
Tokyo's Nikkei average slipped 1.9 percent to a two-week low, as a mass of stocks passed the deadline for buyers to gain rights to first-half dividends.
A further drop in Japanese stocks could fuel speculation about yen-weakening intervention by Japanese authorities to help shore up first-half book closing, keeping traders wary of testing the dollar's downside against the yen, said Yuji Saito, director of foreign exchange at Credit Agricole in Tokyo.
"Selling and buying forces both lack strong momentum, but the market is biased towards selling, with the euro capped by its own problems and the dollar top-heavy against the yen," he said.
The euro hit two-week lows against the yen and the dollar, briefly dipping below 100 yen and falling 0.3 percent to $1.2862.
The yen traded at 77.72 yen, near a one-week high of 77.655 hit on Tuesday, and heavy bids placed at 77.50 yen against the dollar may spur a blip above 78 yen, Saito said.
The dollar index measured against a basket of currencies rose to a two-week high, capping gains in spot gold which was up 0.1 percent to $1,762.06 an ounce.
Protests flared up in Spain on Tuesday ahead of the planned announcement of a new round of unpopular austerity measures for the 2013 budget on Thursday. Spain will also likely set a fresh timetable for economic reforms later this week.
Markets are closely watching Madrid's ability to control its finances, with ballooning regional debts crippling the government's refinancing efforts. The country is also subject to a ratings review by Moody's Investors Service.
Prime Minister Mariano Rajoy is holding back from seeking a sovereign bailout, which would set the stage for the ECB to start buying high-yielding Spanish bonds to ease the country's borrowing costs.
European news and economic data may provide daily trading incentives but markets will largely stick to recent ranges as investors are unwilling to bet on direction until the U.S. presidential election on Nov. 6, said Goro Ohwada, president and CEO at Japan-based fund of hedge funds, Aino Investment Corp.
"Unless it becomes clear which camp is going to win, and unless there is a significantly bad news, nobody's going to take the risk of hastily bailing out of markets. Rather, they are trying to bring their positions close to neutral so they can move quickly after the election result," he said.
Asian credit markets weakened along with other markets, with the spread on the iTraxx Asia ex-Japan investment-grade index widening by 6 basis points.