(Adds Flake, Manchin comments, background)
WASHINGTON, March 8 (Reuters) - U.S. Republican Senator Jeff Flake said on Thursday he would introduce a bill to nullify President Donald Trump's aluminum and steel tariffs, which Trump finalized in a proclamation earlier in the day.
Flake's move came amid a loud chorus of criticism from Republicans, traditionally a free-trade party, for Trump's action. The Republican chairman of the Senate Finance Committee, Orrin Hatch, also criticized the tariffs but said he would work with the White House to "mitigate the damage."
There was some praise from Democrats for the Republican president. Senator Joe Manchin, who is running for re-election this year from West Virginia, where Trump won overwhelmingly in 2016, said it was "past time to defend our interests, our security and our workers in the global economy and that is exactly what the president is proposing with these tariffs."
Flake, an Arizona conservative who has frequently feuded with Trump, said in a statement that Trump's "so-called flexible tariffs are a marriage of two lethal poisons to economic growth protectionism and uncertainty .... Congress cannot be complicit as the administration courts economic disaster."
Flake said he would immediately draft and introduce legislation to nullify the tariffs, "and I urge my colleagues to pass it before this exercise in protectionism inflicts any more damage on the economy."
Trump will impose 25 percent tariffs on steel imports and 10 percent for aluminum but exempted Canada and Mexico.
Both houses of Congress have Republican majorities. But despite widespread unhappiness in the party over Trump's tariffs, passage of such legislation would be a long shot - especially since a two-thirds super-majority would be needed for passage over a likely presidential veto.
Another senator, Republican Mike Lee of Utah, in January introduced a bill to take back some of the power that Congress over the years has delegated to the executive on trade.
Flake, 55, described himself in October as out of step with his party and said he would not seek re-election. His term ends in January 2019.
Although he has voted for Trump's policies, such as the Republican tax overhaul last year, Flake has continued criticizing Trump when he disagrees with him. In a January speech he castigated the president for his attacks on the media.
With Congress stalemated over immigration, Flake earlier this week sought to force a Senate vote on temporarily protecting "Dreamer" immigrants from being deported, while financing Trump's border wall for three years, but another Republican blocked Flake's effort.
(Reporting by David Shepardson; Writing by Makini Brice Editing by Kevin Drawbaugh and Lisa Shumaker)