QALALAN, the Iraq-Iran border — America’s attempts to stem the flood of Iranian fighters crossing into Iraq are being hampered by shortages of supplies and funds for Iraqi border patrols.

One of the most difficult areas to monitor along the 900-mile Iran-Iraq border is the desert plain around Qalalan Castle.

As tensions rise over its role in supplying and training the insurgents, the Tehran government is beefing up its surveillance activities here.

Iran’s border towers include a large four-walled fort on a ridge overlooking the Qalalan plain, bristling with radio antennas, and personnel.

Meanwhile, on the other side of the border, Iraq struggles to maintain a team of 10 uniformed officials at the castle, a turreted two-story building that belies its grand title.

Overseeing border security is an American Army border transition team. But American visits rarely last more than half-an-hour and do little to build confidence that the border is sealed. None of the American soldiers who come here believes that the Iranian forts are there to stop material moving into Iraq.

Instead, one soldier pointed to a town 10 miles away that is a stronghold of the Madhi army, the militia which is supplied with roadside bomb technology and training by Tehran. “The locals have a long tradition of smuggling and can pretty much cross the border whenever they like,” the trooper said.

Each time the American soldiers peer from Qalalan’s walls, they see a stronger Iran. “That’s a new antenna right there,” said Sergeant Marty Cole as he looked east through binoculars. “They’re building up over there. I’m sure it’s for no good.”

The Iraqi guards, who work here in two shifts in teams of five, claim to have mounted night-time ambushes on the smugglers. The obvious question was how many have they caught. “None,” came the answer. An American Army interpreter rolled his eyes, and added, “This is the worst god-damn place on the whole border for smuggling.”

The Iraqi border guards’ only neighbors are the surrounding Iranians. The dirt track leading here winds for miles across the desert, and the nearest town is half-an-hour away.