By Trevor Hunnicutt

NEW YORK, Nov 16 (Reuters) - The U.S. economy could face a recession as soon as 2020 even if lawmakers agree on a spending plan that stokes short-term growth, a top economic adviser to Pacific Investment Management Co said on Wednesday.

Joachim Fels, global economic adviser for Pimco, said it remains unclear whether the policies proposed by President-elect Donald Trump will ramp up growth or rattle the economy.

"One of the strongest conclusions of Trumponomics: we don't know exactly whether Dr. Jekyll or Mr. Hyde wins - whether Trump the expansionist or Trump the protectionist - but what we do know is that under almost any scenario or mix of the two, you get higher inflation," Fels said at the Reuters Global Investment Outlook Summit in New York. "This is what the market has been playing already."

Republicans are widely expected to amp up spending during the Trump administration. But Fels said that fiscal stimulus is not likely to fully hit the economy until 2018, after Republicans have decided what policies to pursue.

Those measures will boost the economy but could ultimately lead the Fed to hike interest rates faster to keep inflation under control in 2019 and 2020, he said.

"Ironically the kinds of policies that are now being discussed - they might actually lead to a recession by the next time the election comes around in four years."

Fels warned that emerging markets may be in for a bumpy ride and that the strength of the U.S. dollar might also start to hurt the economy.

"It's reaching its limits because if you get too much dollar appreciation it feeds back negatively into U.S. growth and particularly hurts the manufacturing sector, and these are Donald Trump's voters, so I think there is a certain limit," said Fels.

"Trump's policies may have some negative impact on the emerging markets if we see more protectionism," or in the unlikely but possible instance that the administration pursues a trade war with China or another country.

BlackRock Inc's chief investment officer of global fixed income Rick Rieder said Monday that he thinks emerging markets are "going to represent a great opportunity going into next year" despite the risks and the fact that many such markets have sold off in recent days.

But betting on inflation is less controversial. Newport Beach, Calif.-based Pimco, which manages $1.6 trillion, went into the Nov. 8 U.S. election with a major holding in Treasury inflation-protected securities. The securities hold their value as inflation increases.

Fels said they feel "comfortable" holding onto TIPS because there is more inflation to come.

(Reporting by Trevor Hunnicutt; Additional reporting by Jonathan Stempel; Editing by Bernard Orr)