VIA CNN

WASHINGTON (AP) -- A Senate breakthrough on an immigration bill praised by leaders in both parties appears endangered by partisan bickering over amendments from opponents.

Both sides acknowledged that if the Senate is going to pass a bill, it might not occur until Congress returns from a two-week Easter recess.

Republicans appeared united in blocking a final vote on a compromise proposal worked out among immigration leaders in the two parties until Democrats allow votes on amendments by opponents.

A test vote was scheduled Friday on the compromise, as well as a bill by Majority Leader Bill Frist.

Democrats said the amendments would undermine the immigration compromise that offered hope for American citizenship for millions of illegal immigrants.

"I know the reality, tomorrow we cannot finish it," the assistant Democratic leader, Sen. Dick Durbin, D-Illinois, said late Thursday.

Supporters of the compromise claimed 70 votes and said they could defeat all of the amendments offered by opponents. Republicans, however, closed ranks in insisting that at least some of those amendments get votes. Both sides indicated the Senate would complete the bill when Congress returns from the recess that begins Monday.