BAGHDAD — Terrorism fears in the United States are all but halting visas for Iraqis, even those who risked their lives aiding the American war effort, making them especially vulnerable ahead of the planned American military withdrawal.

The Obama administration has required new background checks for visa applicants, reacting to a case in Kentucky in which two Iraqi immigrants were arrested on suspicion of ties to an insurgent group, according to American officials in Baghdad.

Advocates say that the administration is ignoring a directive from Congress to draft a contingency plan to expedite visas should those Iraqis who worked for the United States government, especially interpreters for the military, come under increased threat after American forces are drawn down at the end of the year.

“This is not a priority right now for anyone in the government,” said Becca Heller, who runs the Iraqi Refugee Assistance Project at the Urban Justice Center in New York. “Not enough people in the Obama administration care about this topic.”