WASHINGTON - The Senate on Wednesday killed a Republican proposal to require all adult illegal immigrants to return home temporarily in order to qualify for permanent lawful status in this country.

Also defeated was a Democratic bid to restrict legal status to those who have been in the United States for four years.

The vote was 53-45 to table an amendment by Sen. Kay Bailey Hutchison, R-Texas, to require that illegal immigrants go home within two years in order to qualify for a renewable Z visa to live and work lawfully in the United States.

The bill, which could grant lawful status to as many as 12 million illegal immigrants, requires only heads of household seeking permanent legal residency to return home to apply for green cards.

Senators also voted 79-18 to kill a proposal by Democratic Sen. Jim Webb, D-Va., that would have allowed only those who had been in the country for at least four years to gain lawful status. The bill would make anyone here by Jan. 1, 2007 eligible for legalization.

Both amendments were designed to respond to conservatives who decry President Bush's immigration bill as a form of amnesty.

Without her amendment, Hutchison said shortly before the vote, "the amnesty tag that has been put on this bill will remain. It is the key issue in the bill for the American people."

Webb said his proposal would raise the public's comfort level with granting lawful status to illegal immigrants.

"People in this country who traditionally would be supporting fair immigration policies, but who are worried about the legalization process in this bill, would come forward and support this," Webb said.

The revived immigration measure, which also would toughen border security and institute a new system for weeding out illegal immigrants from workplaces, is facing steep challenges from the right and left.

Conservatives call the measure too lenient toward unlawful immigrants, while liberals say it could rip apart families and doom guest workers to exploitation at the hands of unscrupulous employers.

Votes on key amendments were continuing Wednesday afternoon under a complex and carefully orchestrated procedure designed to overcome stalling tactics by conservative foes. It will allow votes only on a limited list of 26 amendments before a critical test-vote on the bill Thursday.

"It's going to be a rough ride," said Sen. Arlen Specter, R-Pa., an architect of the bill. "We're in trench warfare."

Republican framers of the bill were proposing their own, less burdensome return-home requirement for illegal immigrants. It would apply only to heads of household and would give them three years to meet the requirement.

Also expected to be voted on is an amendment by Sen. Kit Bond, R-Mo., that would bar illegal immigrants from eventually getting green cards.

Democratic amendments to give family members of citizens and legal permanent residents more chances to immigrate are also slated for votes.

Conservatives, irate at a process that has essentially stymied their ability to filibuster, said Senate leaders were trying to rush through a bad bill.

"The process has not been a pretty one," said Sen. Jeff Sessions, R-Alabama