Chertoff said in an interview with The Arizona Republic that officials plan to have a total of 370 miles of fencing and 300 miles of vehicle barriers installed by the end of 2008.
Mountains, desert and other harsh terrain span much of the 1,951-mile border.
Before the new fencing was added, there was less than 100 miles of fence along the U.S.-Mexican border, mainly in urban areas.
Congress ordered the administration last fall to build a total of 700 miles of fencing, then gave Homeland Security about $1.2 billion for construction, less than half of what the entire fence would cost.
"We made a commitment (to build 70 miles of fencing this year), and we kept it," said Chertoff, who was in Arizona last week to watch the final sections of fencing go up.
He also attended a meeting of border governors from the United States and Mexico, where fencing and border security are key issues.
"We're not going to overpromise, and it's not going to be a matter of saying we're going to correct a 30-year-old problem (with border security) in a month or even a year, but we are going to set milestones, and we're going to meet the milestones, and we're going to move forward in a deliberate process."
Administration officials say arrests of illegal immigrants along the border have dropped this year, which they believe indicates fewer people are attempting to cross into the country illegally.
But deaths along the border are on pace to exceed last year's total, according to government statistics, which many activists say contradicts the claim of fewer crossings.
Others say a slowing economy, and not government intervention, are responsible for fewer crossings.
Although the fencing is going up on schedule, other initiatives are falling behind.
Homeland Security officials have emphasized the features of a new system, known as a virtual fence, that aims to dot the border with cameras, sensors, observation posts and other high-tech equipment.
Unlike the fencing, that system is not yet ready for use.
A 28-mile test site near Sasabe has had computer and equipment glitches, and the government has not yet approved work done by Boeing, the lead contractor on the project.
Initial testing of the system showed lags between when sensors detected border crossings and when cameras transmitted the information to Border Patrol agents, as well as difficulties transmitting data from the remote sensors and cameras.
Chertoff said he expects Boeing to overcome the problems within the next few weeks.
"We basically said, 'Look, take a couple months, get a new team in, fix this problem,' " Chertoff said. " 'When you feel it's fixed, then we will take it out for a road test, which means we'll operate it, not you.'
"We'll see how it works over a period of three weeks or so. Then, if we're satisfied that it works, we'll accept it. This is prudent buying. You don't actually buy the car until you've taken it out for a fairly extended drive."
New administration efforts to enforce laws against hiring illegal immigrants have also hit some hitches, with a court challenge delaying a proposed rule that would require employers to investigate when workers' Social Security numbers didn't match their names.
"There's no question that you can't do this all at the border, because people are going to keep pushing as long as they can find jobs in the United States that pay a lot more than they get at home," Chertoff said.
Critics said the heavy investment on border security would do little to solve the problem unless authorities cracked down more on employers who break laws by hiring those who do not have permission to work in the U.S.
"We see more fencing going up, and we see more tunnels being dug," said T.J. Bonner, president of the National Border Patrol Council, the union for Border Patrol agents. "We see more inventive ways to go over, under, around the fencing. The front-line agents were never convinced that fencing was the panacea."
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