Administration officials have begun reaching out to steel industry officials in advance of the possible announcement, which is expected to have large repercussions on global trade.

White House aides and others familiar with the issue cautioned that the details of the announcement were still in flux. Administration officials were engaged in a fierce debate Wednesday night about whether to make the announcement Thursday — or delay it altogether, according to the people.

One administration official said aides were still ironing out the legal details of the tariffs, so any announcement is expected to include few details.