* S&P 500 touches 5-week low after sinking 1.2 pct Tuesday
* FTSEurofirst 300 hits roughly 2-week low
* Gold touches three-week peak as investors ditch equities
* Bonds gain as concerns about Washington gridlock grow
* Oil prices lowest since Nov on expanding U.S. inventories (Updates to close of European markets)
By Sam Forgione
NEW YORK, March 22 (Reuters) - Most U.S. and European share indexes fell or were little changed on Wednesday as concerns over potential delays to President Donald Trump's pro-growth policies again unnerved investors, while safe-haven gold, U.S. Treasuries, and the yen rallied.
The benchmark U.S. S&P 500 stock index briefly hit its lowest level in five weeks, while the FTSEurofirst 300 index of top European shares hit a roughly two-week low as investors increasingly worried about whether Trump would be able to push ahead with his pro-growth policies.
Trump on Tuesday tried to rally Republican lawmakers behind a plan to dismantle Obamacare, his first major legislation since assuming office in January. Some investors fear that if the healthcare reform act runs into trouble or takes longer than expected to pass, then Trump's tax reform policies may face setbacks.
Caution continued to prevail a day after the S&P 500 closed down 1.2 percent in its worst daily performance since Oct. 11. CBOE's VIX index, known as the "fear gauge", briefly topped 13 for the first time since mid-January on Wednesday, but was last down 1 percent at 12.31.
U.S. and European shares were little affected by an attack in London near the British parliament which left several people injured and, according to Sky News, two people dead.
"The markets were reminded yesterday the 'Trump trade' is not a one-way trade and there's room for disappointment as actions on tax cuts and infrastructure spending might not materialize as quickly as we want," said Anastasia Amoroso, global market strategist at J.P. Morgan Private Bank in Houston.
"The pronounced fall in yields across the world is not helping market sentiment at the moment either."
MSCI's all-country world equity index was last down 1.33 points, or 0.3 percent, at 446.72.
The Dow Jones Industrial Average was last down 34.5 points, or 0.17 percent, at 20,633.51. The S&P 500 was up 1.08 points, or 0.05 percent, at 2,345.1. The Nasdaq Composite was up 12.26 points, or 0.21 percent, at 5,806.08.
Europe's broad FTSEurofirst 300 index closed down 0.37 percent, at 1,475.46.
The cautious mood stoked demand for gold, U.S. government debt, and the Japanese yen, with spot gold prices touching a three-week high of $1,250.51 an ounce and the dollar hitting a four-month low against the yen of 110.76 yen.
Yields on benchmark 10-year U.S. Treasury notes hit a more than three-week low of 2.375 percent as their prices rallied.
Benchmark Brent crude oil prices fell to a nearly four-month low of $49.71 a barrel and U.S. crude prices hit their own nearly four-month trough of $47.01 a barrel after data showed U.S. crude inventories rising faster than expected, piling pressure on OPEC to extend output cuts beyond June.
The dollar index, which measures the greenback against a basket of six major rivals, was last down 0.2 percent at 99.600 after hitting a nearly seven-week low of 99.563 earlier.
"People are losing confidence in a swift moving set of congressional reform,” said Ian Lyngen, head of U.S. rates strategy at BMO Capital Markets in New York.
Additional reporting by Nigel Stephenson in London, Tanya Agrawal in Bengaluru and Karen Brettell in New York; Editing by Nick Zieminski