A Mexican cross-border truck program could be up and running in four to six months, according to U.S. Trade Representative Ron Kirk.

The optimism follows last week's release of a "concept plan" by Transportation Secretary Ray LaHood for reopening the U.S.-Mexico border to long-distance trucking.

Kirk, speaking at an annual meeting under the North American Free Trade Agreement, said the U.S. "would like to sit down and begin" negotiations with Mexico in the next week, reported the Wall Street Journal.

If that happens, if the U.S. Department of Transportation thinks an agreement to allow cross-border trucking can be reached, and if the U.S. Congress passes corresponding legislation, Kirk said a program could be "up and running as quickly as within the next four to six months," the Journal reported.

In the meantime, Mexico says it will stop rotating its list of retaliatory tariffs. That country's economy minister, Bruno Ferrari, told a news conference the existing list of goods will remain in place without changes until a full agreement is reached between the trade partners, Reuters reported. The effect of the tariffs has been estimated around $2 billion in commercial losses.

Mexico applied the tariffs starting in 2009 after the U.S. Congress halted a demonstration program in which a limited number of trucks were permitted to cross the border into the U.S. interior.

Under the North American Free Trade Agreement, the crossing was supposed to have been opened to border-state traffic in 1995 and to long-distance traffic in 2000. The opening was stalled until 2007 in part by difficult negotiations with Mexico but mainly by U.S. labor unions and owner-operator and citizen advocacy groups that oppose free trade, fear the loss of U.S. jobs and argue that Mexican trucks will not be safe.

In 2007 the Bush administration began a demonstration program under which a limited number of U.S. and Mexican carriers could conduct business across the border, but the program was killed by Congress in 2009.