By Shrutee Sarkar

BENGALURU (Reuters) - The U.S. economy will expand at a robust pace in coming quarters but slow to 2 percent by the end of 2019, according to forecasters polled by Reuters who unanimously said the escalating trade war with China was bad economic policy.

In a sign the trade war is not likely to end any time soon, President Donald Trump on Monday imposed a 10 percent tariff on about $200 billion worth of Chinese imports and threatened duties on around $267 billion more if Beijing retaliates, which it has.

In the meantime, the U.S. economy was forecast to grow at an annualised pace of 3.1 percent this quarter, up slightly from 3.0 percent forecast last month, followed by 2.8 percent in the fourth quarter, according to the latest poll.

All 70 economists who answered an additional question in the Sept 12-19 survey said the trade conflict between the world's top two economies is bad for U.S. growth, posing downside risks to what is otherwise an upbeat outlook for the near-term.

"Absolutely -- it is a bad policy and definitely negative. But it is not bad enough to throw us into a recession, unless it translates to a big negative for confidence and sentiment," said Jim O'Sullivan, chief economist at High Frequency Economics.

"It's kind of like - we have nothing to fear, but we should," O'Sullivan said, trying to describe the delicate situation.

A decade after U.S. investment bank Lehman Brothers collapsed, triggering a devastating financial crisis, the U.S. economic recovery has been unusually lengthy.

Growth is on a solid footing, at least for the near-term, juiced by aggressive tax cuts passed late last year. And a strong labour market underpins the Federal Reserve's plans to raise interest rates further this year and next.

The dollar has surged this year as well and Wall Street is trading near record highs, as many emerging market assets have buckled and retreated.

"The trigger point for the pain is really hard to predict – the stock market has a lot of momentum and optimism but if we keep raising tariffs then it will cause a correction," said Ethan Harris, head of global economics at BofAML.

"It feels like we are in a transition period where the trade war is going from being a minor irritant to a concern, and eventually it will start to impact investment plans."

The latest Reuters consensus for U.S. growth showed slight upgrades for several quarters in the coming year but still is forecasting a slowdown to 2.0 percent in the final quarter of 2019, less than half the last reported rate of 4.2 percent.