UPDATE 1-U.S. aluminum premiums hit near 3-year high after U.S. flags import duty

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* CME aluminum premiums spike to 17 cents/lb from 13 cents/lb

* Premiums like to ease back after kneejerk rise - traders

* U.S. move will displace 1 pct of global aluminum market-CBA (Adds comment, detail)

MELBOURNE, March 2 (Reuters) - Premiums for aluminum metal in the United States spiked to the highest in almost three years after President Donald Trump flagged a 10 percent import duty, as buyers sought to secure metal before higher costs come into force.

Premiums are paid by buyers on top of exchange prices to cover insurance and the cost of delivery, and signal the strength of demand for physical metal.

Trump said on Thursday he would impose duties of 25 percent on steel and 10 percent on aluminum to protect U.S. producers, risking retaliation from major trade partners like China, Europe and neighboring Canada.

Spot premiums for Comex aluminum jumped to 17 cents a pound ($375 a tonne) on Thursday, before finishing at 15.2 cents, up 12 percent and the highest since April 2015.

"I would assume that premiums have jumped because people are saying that it will be harder to get aluminum," said analyst Lachlan Shaw of UBS in Melbourne.

"It seems a bit of a kneejerk over-reaction to me. There will still be metal available, it will just cost more."

Aluminum premiums were also boosted by a lock-out of union workers at an Alcoa smelter in Quebec, which has cut its operation by about two-thirds, said a source at a global producer.

Traders and analysts said premiums would likely settle lower in the short-term, but remain at elevated levels.

Shaw noted the proposed U.S. duty would take the total cost for the 150 kg (330 lbs) of aluminum contained of the average car body to $365 from $330.

Australia's CBA bank said the United States hoped to add about 670,000 tonnes of domestic aluminum output, which would displace about 1 percent of global aluminum production.

"We expect aluminum markets will be able to absorb the impact quite comfortably," CBA said in a report.

The United States imported around 7 million tonnes of crude, semi-manufactured and aluminum scrap, according to U.S. government statistics, mostly from Canada, Russia, the UAE and China.

Some traders had been increasing metal shipments to the United States since December, hoping to cash in on the tariffs, said a source at a metals warehousing company in Singapore.

"A lot of people picked this well ahead, and they reacted early on," he said. "If it hasn't sailed before the end of January it's going to miss the window." Comex aluminum stocks have surged by more than 50 percent this year to 65,327 tonnes. <AL-TTLTTDY-STX> <CMAL0-H18> (Reporting by Melanie Burton; editing by Richard Pullin)