WASHINGTON — President Trump is embracing a new tactic as he tries to rewrite the rules of global trade: Don’t believe a final deal is truly final.

Mr. Trump, who has called deal-making his “art form,” has used his unpredictability as a source of leverage in discussions with Europe, Canada, Mexico, Japan and elsewhere. He has dangled the possibility of lifting American metal tariffs while threatening to add new tariffs on automobiles at any time. He has repeatedly agreed to new trade terms with foreign partners, then talked about undoing those deals to achieve additional goals.

Mr. Trump has argued that this aggressive and unpredictable negotiating style allows him to extract greater economic concessions than past administrations — and he may be right, at least in the short run. But his approach is causing concern among business groups and foreign officials, who say the uncertainty Mr. Trump loves to sow could undermine the role the United States has traditionally played in setting and stabilizing the global rules of trade, hampering economic growth in the process.

His administration is working on a number of trade deals, including agreements with South Korea, Canada and Mexico and discussions with China, Europe and Japan. On Monday, the European Union approved a mandate giving the bloc the authority to negotiate a limited trade agreement with the United States. And Japanese officials met with their American counterparts on Monday in Washington for preliminary trade talks.