NATORI, Japan — Last month, when a team of United States Air Force Special Operations forces reached the damaged Sendai Airport, just a mile from the coast, it found a devastated landscape of uprooted buildings, smashed vehicles and the bodies of the dead.

Using skills honed in war-torn nations like Iraq, the airmen had within hours cleared part of a runway for use by American military aircraft. Over the next four weeks, they worked to restore Sendai Airport, where the huge tsunami had flooded the runway and threatened to engulf the sleek glass terminal.

On Wednesday, the airport in Sendai, one of northern Japan’s largest cities, nearly 200 miles northeast of Tokyo, reopened to commercial flights for the first time since the earthquake and tsunami struck on March 11. But when the airport resumed civilian operations, the two dozen members of the Air Force unit, the 353rd Special Operations Group, were not on hand to celebrate. Nor were most of the 260 Marines and soldiers who also joined the cleanup.

They had already packed up and gone. Their absence reflected the balance the United States military has tried to strike in Japan, where it has undertaken one of its largest relief operations, while also being careful not to be seen as taking a role that might upstage its hosts.