Continued from page 1

“What Tucson is trying to determine, and what some other parts of the border think that they’re at, is what’s their baseline flow — in other words, what do they have to recognize, all other things being equal, is the normal course of illegal crossing activity,” Ms. Meissner said.

She said It’s a difficult balance, since not all crossings are the same.

Some likely represent the same person trying to cross multiple times, while others are high-risk crossers from countries that pose a risk of terrorism. The Border Patrol is trying to grapple with all of those factors in coming up with a new measure of security.

In 2011, the GAO said, the Border Patrol apprehended 327,118 illegal border crossers, while it estimates another 208,813 got away. Of those, 85,827 escaped into the U.S. and the rest turned back.

Auditors cautioned that the numbers are not exact because they often depend on judgment calls about whether someone was deemed to have turned back based on tracks or other signs.

The Border Patrol is still working on numbers for 2012.

But the numbers do show progress from 2006, when the Border Patrol apprehended 1.1 million, while more than 900,000 got away.

President Obama has said he will write immigration legislation this year and submit it to Congress. The legislation is expected to contain a legalization program for the estimated 11 million illegal immigrants in the U.S.

But Steven A. Camarota, research director at the Center for Immigration Studies, said the numbers should be a warning to lawmakers who say the border is secure enough to tackle legalization.

“This doesn’t count the northern border, the coastline, perhaps an equal number of people who overstay temporary visas in the United States,” he said. “The question is, ‘Is that control?’ Most people would say if several hundred thousand people successfully sneak across one of your borders, you’ve still got a serious problem.”

Among other findings, GAO investigators said the rate of repeat offenders has dropped from about 42 percent in 2008 to 36 percent in 2011.

Auditors also said that drug seizures were up 83 percent in 2011 compared with 2006. More than a quarter of that drug activity happened in the Tucson sector.