WASHINGTON -- Senators writing an immigration reform bill are debating whether an actual or "virtual" fence should be built along parts of the U.S.-Mexico border.

Republicans are split on a proposal for a "virtual" fence, using cameras and other technology to monitor illegal traffic. Some want more real fences or walls for long stretches of the line.

Last year, the House passed a measure calling for hundreds of miles of fencing at heavily trafficked areas on the southwestern border and study of a possible fence along the Canadian border.

While discussion about a wall or fence continues, a Senate committee Thursday voted to increase the number of Border Patrol agents, but how many they agreed to add was uncertain.

Senators left a Judiciary Committee hearing with different totals on new agents they want hired. Their figures ranged from 2,000 and 2,400 a year to 10,800 over five years and 12,000 in just two years.

Arizona Democratic Gov. Janet Napolitano Wednesday signed an executive order to expand the National Guard's presence at the state's border with Mexico to combat illegal immigration.

Rep. Jim Kolbe, R-Ariz., who has broken with many House Republican members on building 700 miles of fence between Mexico and the United States, organized a tour of the Arizona border for his colleagues last weekend.

According to the Arizona Republic, the congressmen flew along the border in Border Protection Blackhawk helicopters, toured the region on the ground and talked with Border Patrol and other officials.

Rep. David Dreier, R-Calif., who co-wrote the House bill calling for the border fence, said he was taken aback by seeing the size and scale the project would require.

"I just can't get over how massive this is, compared to (the border) in California," he told the Arizona Republic. "The prospect of a wall is kind of a tough, tough thing."

While the Senators consider the measure, a new poll shows that Californians are about evenly split on whether illegal immigration helps or hurts the state's economy.

The Field Poll found that 47 percent of respondents thought illegal immigration has a favorable impact on the state, while 45 percent believe the opposite.

Back in 1982, just 19 percent thought it was favorable and 75 percent felt it hurt the state.

The poll found registered voters and non-Hispanics were far less likely to find illegal immigration favorable. Non-voters and Hispanics were far more likely to favor immigrants.

Pollsters found among registered voters that only about 25 percent of Republicans see it as positive, while Democrats are more divided.