The sandy streets of Sasabe are empty. Migrant smugglers have to hunt for business at border-town shelters. Deported migrants give up after one try, taking their government up on free bus rides home.

A U.S. crackdown is causing the longest and most significant drop in illegal migration from Mexico since the Sept. 11 attacks. Officials say the U.S. economic downturn, tighter security and a more perilous and expensive journey are persuading many who try to sneak into the U.S. to give up sooner.

Border Patrol arrests are down 17 percent so far this year along the U.S.-Mexico border after falling 20 percent all of last fiscal year and 8 percent the year before that. While it's impossible to know how many people are crossing illegally, the Patrol uses approximations to estimate the ebb and flow of traffic.

The downturn in illegal immigration has created labor shortages throughout the United States and several states are considering temporary-worker programs, especially in agricultural fields, where produce is going bad.

Mexicans in the United States are starting to send less money home, too.

Remittances soared in the early part of the decade to become Mexico's largest source of foreign income after oil exports. But they rose just 1 percent in 2007, reaching $24 billion and in the first quarter this year, they slipped almost 3 percent from the same period last year, Mexico's central bank said this week.

Adolfo Vasquez, a 41-year-old corn farmer from southern Mexico, picked fruit for three years in Washington state. Last year it took him two tries to get to his job. This year, he walked for four nights before U.S. Border Patrol agents caught him. He doesn't plan to try again.

''It's very disheartening because every time it gets twice as difficult,'' said Vasquez, resting under an aid station tent for deportees in Nogales. ``We're going to go to Los Cabos or Tijuana. We hear there is work there.''

The number of returned migrants who try again through the heavily traveled desert corridor west of Sasabe has dropped from 80 percent to 40 percent since January, said Border Patrol spokesman Jose Gonzalez. Agents keep fingerprints on all those apprehended and can determine multiple offenders, even if they give false names.

U.S. authorities attribute the drop to tighter security and a new program in the Tucson sector that has prosecuted more than 3,000 migrants for crossing illegally since it started in January. They face jail sentences from a few days to six months.

But none of the migrants interviewed by The Associated Press knew about the new prosecution program. Those on their way home said the main deterrents were tougher security and the dangers of the desert, including bandits who rob and even rape migrants on both sides of the border.

The U.S. Border Patrol has added 200 officers since last year to the Tucson sector, and a total of 3,000 agents now search the vast desert for illegal migrants by truck, horse, ATV and helicopter. They now have four drones scanning for drug and migrant smugglers, as well as two newly built 12-foot walls with steel posts near Nogales and Sasabe.

At the same time, Mexican drug smugglers have started to collect fees for access to the main routes into Arizona.

As a result, Grupo Beta, the Mexican government's migrant rescue group, has seen a 257 percent increase in the number of people seeking discounted bus tickets home this year. So far, 2,500 people in Nogales and Sasabe asked for the tickets this year, while Grupo Beta had only 700 requests in all of 2007.

''We can't keep up with so many people who are heading back,'' said Enrique Enriquez, coordinator for Grupo Beta in Nogales. He said his rescuers spend the day shuttling migrants to a bus station.

Maria Fernández, 25, made her first crossing with her husband after both had been laid off from a department store in Puebla state. Friends in New York offered to help them find work. First they traveled to Altar, a farming town 70 miles south of Sasabe, a major gathering point for those heading to Arizona.

There, they had to pay about $50 so drug smugglers would allow them to travel the bumpy road north, and another $30 for a van that took them and another 25 migrants to Sasabe.

They walked for four nights through the mesquite-covered desert, where they were robbed once. They hid from Border Patrol agents at least five times. But when they reached the highway where they would meet their next ride, they were spotted by a helicopter.

Now, Fernández was waiting in Nogales for her husband to be deported, as she had been.

''I won't try again because it's very difficult and, as a woman, one risks a lot,'' she said.

The crackdown has made smugglers more desperate to recruit clients for the trip north. If fewer people cross, their earnings drop.

Francisco Loureiro, who runs a migrant shelter in Nogales, said that when migrants began arriving in January, the start of the high season, he spotted smugglers trying to drum up business inside his shelter.

Now, local police visit the shelter three times a night.

''The officers have found smugglers carrying guns and even drugs,'' Loureiro said.

During earlier peak traffic seasons, overflowing vans and pickups would arrive in Sasabe and then head out to the drop-off points where migrants begin their long walk. The town of 1,500 people could see its population triple from migrants passing through.

Now businesses are closing and at least six safe houses and hotels have been left unfinished, said town administrator Ramona Flores. Border experts estimate that 70 percent of residents earn their living from migration.

On a recent afternoon, only eight men waited for their smuggler near a pile of smashed and rusting cars.

''We're supposed to be in high season, but in one day the most we've seen is between 300 and 400 migrants,'' Flores said.

Juan Luna, a 39-year-old bricklayer from Guanajuato state, said he was heading to Oklahoma, where he would work as a dishwasher at a restaurant. But after two nights of walking through the desert, he and five others from his town were caught.

''The United States is where those without resources go,'' Luna said at the Nogales bus station, where he was waiting to return home. ``That was a little door we still had open. But they are closing it, and now we don't know what we will do.''