(Adds comments, details from news conference)
By David Lawder
WASHINGTON, Jan 16 (Reuters) - The International Monetary Fund on Monday said the U.S. economy would grow faster than previously expected in 2017 and 2018 based on the incoming Trump administration's tax and spending plans, but it kept its global growth forecasts unchanged due to weakness in some emerging markets.
Updating its World Economic Outlook, the IMF forecast overall global growth at 3.4 percent for 2017 and 3.6 percent for 2018, unchanged from October. That compared to 3.1 percent in 2016, the weakest year since the 2007-2009 financial crisis.
It estimated a modest fiscal stimulus under President-elect Donald Trump would push U.S. gross domestic product growth to 2.3 percent in 2017, a gain of 0.1 percentage point on the last forecast, and to 2.5 percent in 2018, up 0.4 percentage point.
The IMF noted, however, that Trump's plans for expansionary fiscal measures including tax cuts and infrastructure spending also could stoke inflation in an economy already nearing full employment.
"If a fiscally-driven demand increase collides with more rigid capacity constraints, a steeper path for interest rates will be necessary to contain inflation, the dollar will appreciate sharply, real growth will be lower, budget pressure will increase, and the U.S. current account deficit will widen," IMF chief economist Maurice Obstfeld said in a statement.
That would increase the likelihood of more protectionist U.S. trade measures and retaliatory responses, Obstfeld told a news conference.
"In that scenario, all countries would lose out," he added.
But the new IMF outlook does not include any assumptions regarding Trump's trade plans, such as potential tariffs on Mexican and Chinese goods, as there seems to be less of a political consensus surrounding them, Obstfeld said.
The IMF does assume a stronger dollar, firmer oil prices and "more inflationary pressure and a less-gradual normalization of U.S. monetary policy."
While stronger oil and commodity prices have improved the picture for oil exporters including Nigeria, higher interest rates and tighter financial conditions will negatively affect many emerging market economies, including Mexico and Brazil.
The IMF cut Mexico's growth forecasts by 0.6 percentage point in both 2017 and 2018, citing a consumer spending pullback amid worries about Trump's trade policies.
The IMF revised its 2017 growth forecast for China to 6.5 percent, up 0.3 percentage point from October, based on expectations for continued stimulative government policies, but left unchanged its 2018 forecast for a slowdown to 6.0 percent growth.
The Fund said China's reliance on stimulus, rapid expansion of debt and slow progress in dealing with corporate debt "raises the risk of a sharper slowdown or disruptive adjustment."
India, which has recorded some of the world's strongest recent growth, is experiencing a shock to consumption from the government's decision to withdraw larger currency notes from circulation, chopping a full percentage point off the IMF's fiscal 2016-2017 growth outlook to 6.6 percent.
The Fund trimmed its fiscal 2017-2018 forecast for India to 7.6 percent from 7.2 percent.
The IMF raised its 2017 forecasts for the euro zone and Japan by 0.1 percentage point each, largely because of stronger-than-expected results in the second half of 2016. Britain's forecast was increased 0.4 percentage point, but its 2018 growth was reduced by 0.3 percentage points.
The IMF said the risks were tilted to the downside, with potential factors including protectionist policies, tighter financial conditions, banking system stress in Europe and increased geopolitical tensions.
But it noted there was potential for upside growth surprises if policy stimulus in the United States or China turned out to be larger than currently projected. It said it expects more certainty over the direction of U.S. policy by the time of the next full World Economic Outlook in April. (Reporting by David Lawder; Editing by Kim Coghill and Paul Simao)