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The UAE Embassy in Washington referred questions to Etihad Airways, the UAE’s national carrier and the only airline with regular service to the U.S. from Abu Dhabi. The airline, which is owned by the Abu Dhabi royal family, did not return calls.

In addition to streamlining arrivals for international air travelers while screening them for security purposes, officials say, the centers reduce pressure on arrival checkpoints at overloaded destinations such as O’Hare International Airport in Chicago or the John F. Kennedy International Airport in New York. CBP now operates 14 pre-clearance facilities: eight at Canada’s major airports, two each in the Bahamas and Ireland, and one apiece in Bermuda and Aruba.

Congress ordered the expansion of the pre-clearance system after the Sept. 11, 2001, terrorist attacks involving hijacked airliners, but no centers have opened since 2006, in part because they are expensive to build, operate and staff. Moreover, U.S. officials generally insist that CBP personnel at pre-clearance centers operate armed and with full legal authority — a measure that few countries are willing to allow.

The center is likely to be a boon for Etihad Airways, and some U.S. airlines have argued that a pre-clearance center at the desert outpost would give Etihad an unfair advantage over domestic carriers and other foreign airlines.

If established, U.S.-bound travelers from Africa, Asia and Eastern Europe will have a choice of connecting to Etihad in Abu Dhabi, where they can pre-clear customs checks; or connecting to a carrier at a different hub, which could result in significant delays at U.S. customs centers.

Ms. Napolitano has said the center’s success should be measured by how much it boosts airline traffic in Abu Dhabi, which has lagged Dubai as the commercial and trading hub for the seven emirates.

In December 2011, just days after signing a letter of intent with the UAE, she told an audience at the Council on Foreign Relations, “I think we’ll see travelers move to the pre-cleared routes. I think you’ll measure [success] by how travel routes adjust.”

Reps. Patrick Meehan, Pennsylvania Republican, and Peter A. DeFazio, Oregon Democrat, introduced a bill last month that would require Homeland Security to provide Congress with an economic impact assessment before opening another pre-clearance site.

Also in November, Rep. Sheila Jackson Lee, Texas Democrat, and Rep. Bennie G. Thompson, Mississippi Democrat, introduced a bill that would require a security assessment before pre-clearance operations can be expanded to more countries or airports and would preclude a foreign government or entity from paying for such operations, as is planned for Abu Dhabi.

In congressional testimony, CBP officials estimated the total annual cost of an Abu Dhabi pre-clearance center to be $5 million, but said the UAE airports authority would reimburse costs up to the legal limit, leaving CBP to pay less than $500,000 a year.

In April, Mr. Thompson, Mrs. Lee and 12 others wrote to Ms. Napolitano, expressing concern that the proposed center “sets a dangerous precedent of deploying customs resources based on the availability of third-party financing — not national security, common sense, or the needs of traveling taxpayers.”

The letter raised numerous questions regarding security risks and benefits and the extent of CBP’s involvement in the negotiations. Many of those questions remain unanswered, said congressional sources who reviewed Homeland Security responses restricted from public release.

Some analysts have defended the proposal.

Jayson Ahern, a principal of Beltway security consultants the Chertoff Group and a 33-year veteran of the CBP and the U.S. Customs Service, said foreign terrorists continue to be fascinated with aviation as a target.

He characterized a pre-clearance center in Abu Dhabi, staffed by armed CBP agents with “full law enforcement authority” and reimbursed by the UAE up to 85 percent of its cost, as a great deal.

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