Senators working out an immigration overhaul bill Thursday agreed to further 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.

"Over 10,000, I think is a safe reference," said Blain 1/4, a spokesman for the committee. He said aides were going through transcripts trying to figure out the correct number.

The confusion reflects the complexity of the immigration legislation that the committee is trying to push to full Senate by March 27.

The House in December approved a bill that calls for hiring 1,000 new agents in 2006.

An intelligence overhaul that Congress passed in late 2004 recommended adding 2,000 more agents a year over five years, to boost the Border Patrol to about 20,000 agents.

Since then, however, Congress has funded only 1,500 additional agents.

"I do believe the numbers are not adequate to achieve the numbers at the border that we want to achieve," said Sen. Jeff Sessions, R-Ala.

The Border Patrol has increased from 8,351 agents in 1999 to about 11,300 now. Last year, the agency apprehended about 1.2 million illegal immigrants, compared with 1.6 million in 1999.

A report this week by the Pew Hispanic Center estimated the illegal immigrant population has grown from about 8.4 million in 2000 to between 11.5 million and 12 million as of a year ago this month

Deborah Meyers, a senior policy analyst with the Migration Policy Institute, said the size of the undocumented population is a better measure of effectiveness.

"A policy that has focused solely on the border has not been successful in terms of reducing the flow of undocumented immigrants to the United States and one of the things we are seeing in legislation is the much greater role work site enforcement has to play in controlling undocumented migration," Meyers said. Her Washington-based think tank tends to favor immigration.

Also Thursday, the committee approved or accepted:

—Amendments sponsored by Sessions and Sen. Tom Coburn, R-Okla., to require detention and expedited deportation of apprehended non-Mexican immigrants.

—An amendment by Sen. John Cornyn, R-Texas, prohibiting immigrants convicted of rape or child abuse from bringing spouses to the United States.

—An amendment by Sen. Jon Kyl, R-Ariz., to authorize fencing and other barriers for his state's border with Mexico and an amendment by Sen. Ted Kennedy, D-Mass., to do a border fence study.