WASHINGTON - The chairman of the House Homeland Security Committee asked the Obama administration Friday to provide data to back up its assertions that the Southwest border is more secure than it has been in decades.

In a letter to Janet Napolitano, secretary of Homeland Security, Rep. Michael McCaul, R-Texas, said the administration's claims of success on the border appeared at odds with a Los Angeles Times story Thursday that cited details from internal Customs and Border Patrol reports.

"These revelations are in stark contrast to the administration's declaration that the border is more secure than ever due to greater resources having been deployed to the region, and that lower rates of apprehensions signify fewer individuals are crossing," McCaul wrote.

McCaul said Congress has provided money over the last decade to more than double the number of border agents, build nearly 700 miles of fencing and deploy new surveillance technologies.

"However, we do not know if additional resources have produced better results," he wrote. He said the administration has been "unable to answer the fundamental question: How effective are we at keeping illegal immigrants, drug smugglers and potential terrorists out of our country given this enormous investment?"

Rep. Candice Miller, R-Mich., who chairs the House Subcommittee on Border and Maritime Security, also signed the letter. Peter Boogaard, the Homeland Security Department spokesman, said Napolitano's office will respond directly to the members of Congress who sent the letter.

The Times story quoted internal reports on Vader, short for Vehicle and Dismount Exploitation Radar. The system, which is mounted on a Predator drone, tracks people on the ground. Border Patrol agents are then sent to intercept them.

The internal reports showed that border agents apprehended fewer than half of the individuals who the airborne radar showed had illegally crossed into a 150-square-mile stretch of Arizona west of Nogales between Oct. 1 and Jan. 17.

In interviews, Customs and Border Protection officials said the internal reports are misleading because the tallies include only those migrants and smugglers who were tracked and captured when the radar was operating, and not those who may have entered or been captured when the Predator was elsewhere or on the ground.

The Vader system is used about two weeks every month, usually starting in predawn darkness and flying eight to 12 hours.

The officials also said the radar is operated on a remote part of the 2,000-mile border, and the results may not be indicative of apprehensions in other areas.

"The initial methodology for apprehensions and turn-backs reported was flawed and reflected an incomplete picture of border enforcement actions," said Michael Friel, spokesman for Customs and Border Protection.

"Apprehensions in the report reflected enforcement actions during the limited hours that the Vader system was deployed and did not reflect apprehensions made outside (its) view," he added.

The agency is working to refine the methodology and to expand use of Vader to other parts of the border, however.

It has requested money from Congress for two more Vader systems. Each costs about $5 million a year to maintain and operate.

The radar, which was developed by the Pentagon to help U.S. forces spot insurgents planting roadside bombs in Afghanistan, has been deployed in Arizona for about 1,300 hours since March 2012.