* Record highs on Wall St, driven by tax bill hopes, M&A flurry
* Dollar under pressure on U.S. tax reform concerns
* Oil gains as Forties outage, Nigeria strike threaten supply
* Gold ticks higher as nerves over U.S. tax bill hit dollar
* U.S. yield curve flattening marches on (Updates with open of U.S. markets; changes byline, dateline; previous LONDON)
NEW YORK, Dec 18 (Reuters) - Top world stock markets climbed to record highs on Monday as U.S. Republican lawmakers moved closer to passing a tax plan, while the dollar slid on concerns about the bill's impact on economic growth and interest rates.
Leading Republicans said they expected Congress to vote as early as Tuesday on the bill, which would become the biggest U.S. tax code overhaul in more than three decades if approved. President Donald Trump is aiming to sign the plan into law at the end of the week.
Wall Street's leading indices struck all-time highs in early trading ahead of a potential vote, which would lower the corporate income tax rate to 21 percent from 35 percent.
"The market is going to continue its rally based on the belief that we're going to see the Congress pass tax reform," said Robert Pavlik, Chief Investment Strategist at SlateStone Wealth in New York.
The Dow Jones Industrial Average rose 183.5 points, or 0.74 percent, to 24,835.24, the S&P 500 gained 17.09 points, or 0.64 percent, to 2,692.9 and the Nasdaq Composite added 58.03 points, or 0.84 percent, to 6,994.61
The benchmark MSCI World index, which tracks stocks around the globe, gained 0.97 percent to a record high. The pan-European FTSEurofirst 300 index rose 1.19 percent.
Meanwhile, the dollar index fell 0.39 percent after initially inching up following the tax plan's latest advancement.
U.S. currency traders began to speculate how impactful the pro-growth bill could be and whether it would accelerate interest rate increases by the U.S. Federal Reserve, above the two currently anticipated by the market.
The euro was up 0.44 percent to $1.1804.
The greenback's weakening propelled gold higher as the dollar-denominated bullion became cheaper for buyers using other currencies.
Spot gold added 0.6 percent to $1,262.52 an ounce. U.S. gold futures gained 0.67 percent to $1,265.90 an ounce.
The gap between U.S. shorter-dated and longer-dated Treasury yields contracted to its smallest in a decade on expectations the government would increase its short-term borrowing with the possible passage of the tax cut bill.
Oil prices rose amid an ongoing North Sea pipeline outage and as a strike by Nigerian oil workers threatened the country's crude exports. U.S. crude rose 0.19 percent to $57.41 per barrel and Brent was last at $63.46, up 0.36 percent on the day.
Bitcoin was down 1.3 percent to $18,703.96 on the Bitstamp exchange after rising to a record of $19,666 over the weekend, ahead of CME Group Inc's launch of bitcoin futures on Sunday.
(Additional reporting by Alasdair Pal in London; Editing by Nick Zieminski)