In addition, critics say building a fence on the nation's border would give the wrong impression about the United States.
"It just harkens back to the Chinese wall and the Berlin Wall, not the message we want to send to the Mexican government, the Canadian government, and the rest of the world," said John P. Clark, deputy assistant secretary of Immigration and Customs Enforcement.
Rep. Duncan Hunter, R-Calif., the chairman of the House Armed Services Committee, introduced legislation last week to build a 2,000-mile long high-tech security fence from the Pacific Ocean to the Gulf of Mexico.
It would include a double fence with lighting and sensors and be surrounded by a 100-yard security zone.
Joe Kasper, a spokesman for Hunter, said that the barrier is needed — as part of a larger strategy — because illegal immigration is a pressing national security issue.
"We have an illegal immigration problem in our country and we need to take action for ourselves and not for global opinion," he said.
An estimated 11 million illegal immigrants live in the United States and the number is growing.
Several groups, including the Philadelphia-area organization Let Freedom Ring, have lobbied for a border fence as the only way to control the porous borders. The group has pushed for a fence on its Website — weneedafence.com — and in television commercials.
The group believes the fence should resemble the one Israelis are building along the West Bank with coils of barbed wire, a ditch, two wire fences, sensors, closed circuit TV cameras and motion detectors.
Currently, there are some fenced areas with barbed wire near U.S. border crossings, but most of the Southern border is open. The Department of Homeland Security recently approved the completion of a 14-mile border fence near San Diego, which had been stalled for years because of lawsuits from environmental groups.
One of the main problems with building such a fence across the entire Southern border is the price tag.
Kasper said that there is no official government estimate on the cost of the fence, but that it would probably be about $1 million per mile or roughly $2 billion total. Others estimate the price much higher at around $8 billion.
Hunter believes the expense is worth it because a fence would ensure the nation's security and would eventually offset the large costs of illegal immigration, including costs in healthcare and education, Kasper said.
But T.J. Bonner, president of the National Border Patrol Council, the union that represents agents, said building a fence is one of many "band-aid solutions" that doesn't address the root-cause of the problem — desperate people seeking work.
"As long as employers hire them, they'll figure out a way to come," said Bonner, who has been a Border Patrol agent for nearly 28 years.
In addition, he said that the billions of dollars a fence would cost would be better spent cracking down on employers who hire illegal immigrants and establishing a new counterfeit-proof identification document that businesses could use to prove their employees' citizenship.
Michael O'Hanlon, a senior fellow and homeland security expert at the Brookings Institution in Washington, said that building a fence is difficult, but worth discussing.
It must be done, however, in a way that would not hurt the relationship between the United States and Mexico, he added.
The federal government could offer more citizenship applications or visas for Mexican immigrants as part of a broader plan, O'Hanlon said.
But Clark said that building a fence would hurt the cooperative law enforcement relationship between the two countries, which has improved over the past few years and has led to successful investigations of large drug smuggling and human trafficking operations.
Kasper countered that the border fence near San Diego has helped authorities on both sides of the border apprehend criminals.
Sen. John Cornyn, a Texas Republican who chairs the Immigration, Border and Citizenship Subcommittee, said that a physical barrier in some locations makes sense, but that "a 2,000-mile-long fence along the entire southern border - including in remote, barren locations - is a 19th century answer to a 21st century problem."
Cornyn and other lawmakers believe that a comprehensive strategy is needed to fix the nation's immigration system, including the establishment of a temporary worker plan that would allow immigrants to work in the United States legally for a number of years.
A bill by Cornyn and Sen. Jon Kyl, R-Ariz., includes border security measures — such as adding 10,000 border patrol agents over the next five years — as well as a temporary worker plan. Current illegal immigrants would have to return to their home countries to apply for the temporary visas.
President Bush also supports a temporary worker plan, although he hasn't endorsed any specific legislation in Congress.
Homeland Secretary Michael Chertoff did say, however, that the administration does not support sealing the entire Southern border.
"Let me be clear — we will not build a giant wall across our borders," he said last week. "But in areas where it makes sense to do so, we will look at physical infrastructure and technology improvements to deter illegal border crossings."