WASHINGTON  The administration has no present plans to reopen negotiations on the North American Free Trade Agreement to add labor and environmental protections, as President Obama vowed to do during his campaign, the top trade official said on Monday.

“The president has said we will look at all of our options, but I think they can be addressed without having to reopen the agreement,” said the official, Ronald Kirk, the United States trade representative. It was perhaps the clearest indication yet of the administration’s thinking on whether to reopen the core agreement to add labor and environmental rules.

Mr. Kirk spoke in a conference call with reporters after returning from a regional summit meeting that Mr. Obama attended over the weekend in Trinidad. He said that Mr. Obama had conferred with the leaders of Mexico and Canada  the other parties to the trade agreement  and that “they are all of the mind we should look for opportunities to strengthen Nafta.”

But while he said that a formal review of the 1992 pact had yet to be completed, Mr. Kirk noted that both Mr. Obama and President Felipe Calderon of Mexico had said that “they don’t believe we have to reopen the agreement now.”