Washington ? Republicans and Democrats placed strict new conditions on a broad immigration measure Wednesday, as the White House and the bipartisan group that crafted it fought to keep their compromise intact.

The Senate voted overwhelmingly to slash the number of foreign workers who could come to the U.S. on temporary visas. It also endorsed toughening the security measures that would have to be in place before millions of illegal immigrants could begin gaining permanent legal status or a new temporary worker program could be launched.

The measure faced new challenges as Democrats sought to loosen its limits on family-based immigration and Republicans proposed further security measures.

The guest worker program would be capped at 200,000 a year under the Democratic proposal approved Wednesday, which passed 74-24 over strong opposition by the Bush administration.

Commerce Secretary Carlos Gutierrez said the change, proposed by Sen. Jeff Bingaman, D-N.M., would interfere with a “central component” of the White House-backed immigration measure. That plan provided for 400,000 worker visas annually, plus an option to increase that number to 600,000 if market conditions demand it.

“The Bingaman amendment would eliminate this critical flexibility and cut the size of the temporary worker program in half,” Gutierrez said in a statement.

Senators approved a proposal by Republican Sen. Judd Gregg of New Hampshire to toughen the bill’s so-called triggers, which condition the temporary worker program and the granting of legal status to illegal immigrants to strict border security and workplace enforcement measures.

They also adopted a proposal by Sen. Lindsey Graham, R-S.C., to crack down with mandatory prison sentences on illegal immigrants who re-enter the U.S.