The Senate will consider a bill calling for erecting 700 miles of fencing on the U.S-Mexican border, a proposal that has been approved twice by the House.

Senate Majority Leader Bill Frist, R-Tenn., used a legislative maneuver to get the bill to the floor as early as Wednesday, when the Senate could decide whether to move forward on the legislation.

"Border security is the essential first step of any effort to enact immigration reform. Only when we have convinced the American people of our commitment to securing our borders will we be able reach a consensus on comprehensive immigration reform," Frist said in a statement.

Democrats are likely to try to block the bill. They may try to attach the comprehensive immigration bill the Senate passed in May as an amendment and push debate into next week. A delay could be a problem as Congress tries to wrestle with legislation addressing treatment of terrorism suspects.

"This smacks of desperation and a clear repudiation of President Bush's support for comprehensive immigration reform. It's obviously designed to play to the base. Sen. Frist was for comprehensive immigration reform before he was against it," said Jim Manley, spokesman for Senate Minority Leader Harry Reid, D-Nev.

House Republicans, trying to keep the illegal immigration issue before voters, passed the fence bill last week by a vote of 283-138. The House had approved the same amount of fencing last December as part of a broader bill that would have made being in the country illegally a felony. That bill is stalled.

The nearly 2,000-mile U.S.-Mexican border now has about 75 miles of fencing.

The Senate's immigration bill calls for 370 miles of triple-layer fencing along the Mexican border. The Senate approved $1.8 billion in a defense spending bill for the construction. The House has not provided funding for the fence it approved.

The House and Senate passed far different immigration bills. Republican leaders in the House have resisted compromise. Heading into elections, they chose instead to take out parts of their bill and pass them separately to keep the focus on border security, which plays well with conservative voters.

The fence bill to be considered in the Senate is HR 6061.