For the third straight summer, some illegal immigrants who have been caught crossing the U.S.-Mexico border are being flown back home.

The flights, part of the Homeland Security Department's so-called repatriation program, aim to reduce the chances of migrants recrossing the porous Arizona border by flying them deep into the interior of Mexico.

The first repatriation flight this year carried 67 people to Mexico City on Friday. From there, they were to be bused to their home communities in central and southern Mexico, officials said.

The program targets immigrants deemed at physical risk if they tried to cross the border through the desert again, including those who are close to dehydration, are exhausted or in need of medical attention, said Russell Ahr, a spokesman in Phoenix for U.S. Immigration and Customs Enforcement.

It also targets women and children, particularly women who might be pregnant, Ahr said.

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"This is a voluntary program, so they are screened both by agency and consular officials from Mexico to make sure they fit the criteria for the program and are willing participants," he said.

Illegal immigrants identified as criminals are not eligible to participate in the program, nor are minors unaccompanied by adult relatives, Ahr said.

Federal officials hope to decrease the number of migrant deaths in the Arizona desert and to try to disrupt border smuggling activities by "reducing the number of people who get recycled," he said. Many who are returned to Mexican border cities immediately encounter smugglers or paid guides and come back to the United States.

The flights are operated by Aeromexico as a subcontractor for CSI Aviation Services. There will be two daily flights, carrying up to 300 people in all.

The program lasted 81 days in 2004, returning 14,067 people on 151 flights at a cost of about $15 million, Ahr said. Last summer, the program ran for 113 days, repatriating 20,592 people aboard 225 flights. It cost $13.6 million.

Immigrants rights groups charge the program is expensive and ineffective. Critics say the money would be better spent by installing water stations and rescue beacons in the desert.