McALLEN, Texas - The first reminder that human cargo was still steadily moving north from Mexico came in July, when more than 40 people, two of them dead, were found in a truck in Dallas. Then in August, border agents in Sarita, Texas, found 73 men, women and children alive and packed in a tractor-trailer filled with rotten watermelons.

Then in October, in Iowa, the skeletons of 11 people, some later identified as Mexican laborers, were discovered in a locked car of the train that had ferried them north. Weeks later, border agents in Laredo, Texas, found 51 people, uncomfortable but breathing, in a tractor-trailer that had tried to slip past a checkpoint.

The incidents offer vivid evidence that the abrupt slowdown in illegal immigration after the Sept. 11 attacks is over. So do recent statistics compiled by the U.S. Border Patrol, which show that apprehensions of illegal immigrants - the barometer for measuring activity along the border - are roughly back to where they were before Sept. 11.

"We're running about even with last year, maybe slightly higher," said Ray Garza, assistant chief of the Border Patrol's McAllen sector, which covers south Texas.

Garza and other officials added that tightened security along the border had made the crossing more dangerous and expensive, since the services of smugglers, known as "coyotes," were now almost always required. The people found in the truck in Dallas, for example, had each paid $1,500 to $2,000, a huge sum for someone who might be lucky to find a $6-an-hour job in this country.

Mario Villarreal, a Border Patrol spokesman in Washington, said the inflated smuggling fees were the result of the increased difficulty of crossing the Rio Grande after a huge expansion of border agents in the 1990s.

"Smuggling fees basically used to be whatever you had," Villarreal said. "It could be $20 or $40. But because of the increased enforcement, it's much harder to enter the United States, and that has driven fees up from $1,000 to $2,000 per person from Mexico."

Border Patrol officials often characterize smuggling rings as large, sophisticated operations that are sometimes intertwined with drug-trafficking operations. Villarreal said one smuggling ring was known to send a group of illegal immigrants in one direction as a decoy.

But some analysts contend that the image of a high-tech human smuggling ring can be misleading. Often, they say, smuggling rings may be a handful of family members or acquaintances who own safe houses along the route north.

One woman in south Texas, whose nephew used a smuggler to cross, said the local rings often communicated by cell phones and pagers, tipping off one another to patrols. The woman, who would allow the use only of her given name, Elizabeth, said the smugglers falsified documents to help people pass checkpoints on the international bridges.

The biggest crackdown occurred after Sept. 11, when crossing on border bridges ground to a virtual halt. Trips that had previously taken a half hour suddenly took half a day. And the number of apprehensions plummeted, falling 25 percent during the 2002 fiscal year.

Gradually, numbers have been returning to previous levels.