US immigration reform trumped by election year politics: Experts

"Politics got ahead of policy on this," lamented Democratic Senator Edward Kennedy, a key proponent of a compromise Senate bill.

"It's not going forward because there's a political advantage for Democrats not to have an immigration bill," added Republican Senator Arlen Specter.

The senators spoke after their colleagues failed Friday to approve a compromise immigration bill brokered by Republican and Democratic Party leaders, indefinitely delaying any attempt to plug the porous US borders or address the status of nearly 12 million illegal immigrants already in the United States.

With lawmakers headed out on a two-week break, it was not clear when they would resume the debate, which has deeply divided Republicans controlling the Senate.

Democrats appeared to be watching the clock ahead of the recess, and announced they had blocked debate on hundreds of amendments to the bill for fear they would drastically alter it.

Republicans and US President George W. Bush were swift to lay blame with the Democrats.

"Unfortunately the Senate minority leader prevented voices from being heard and amendments from being considered. He is preventing comprehensive immigration reform from moving forward," White House spokesman Scott McClellan accused.

But political scientists consulted by AFP applauded Democrats for taking advantage of deep divisions within the Republican majority in an election year.