By David Lawder

WASHINGTON, March 9 (Reuters) - The owner of a shuttered aluminum smelter in southeastern Missouri said on Friday the firm would restart two of the plant's three production lines following President Donald Trump's decision to impose tariffs of 10 percent on imported aluminum and 25 percent on steel.

Magnitude 7 Metals LLC, founded by former Glencore Plc aluminum trader Matt Lucke, said in a statement that work was under way to prepare the first production "potline" to restart in the second quarter of 2018, with a second potline ready to restart in the third quarter.

It did not identify the number of workers who would be rehired, but State Representative Don Rone said in a news release that the company expected to recall about 400 workers at the plant in Marston, Missouri.

Some 900 workers at the plant were laid off when its previous owner, Noranda Aluminum, ceased production and filed for bankruptcy protection in 2016 under pressure from rapidly expanding Chinese aluminum imports.

"M7M hopes to soon be in a position to expand its restart plans to cover additional primary production capacity and/or downstream operations at the smelter site, with significant additional employment levels included," the company said in a statement.

ARG International AG, a Swiss-based company set up by Lucke, acquired the smelter with a primary aluminum capacity of 263,000 metric tons per year for $13.7 million in a bankruptcy court-approved deal.

ARG will operate the smelter through Magnitude 7, a subsidiary named for a series of earthquakes in 1811 and 1812 in nearby New Madrid, Missouri.

In May 2017, the Missouri legislature approved a plan to allow large power utility customers including Magnitude 7 to negotiate cheaper electricity rates. The plan was aimed at encouraging a restart of the idled smelter and attracting electric-arc furnace steel makers to the state. Nucor Corp announced last month it would open a reinforcing bar "micro-mill" in Sedalia, Missouri, in 2019, providing about 250 full-time jobs.

Magnitude 7 said it was "prepared to move quickly on additional projects, including potentially the restart of the third and final potline of primary production capacity, if and when market conditions allow."

But Trump's tariffs on Friday began to ease further as more U.S. allies clamored for exemptions similar to those granted to Canada and Mexico. (Reporting by David Lawder Editing by Leslie Adler)