WASHINGTON -- With the Senate beginning debate Monday on a far-reaching immigration overhaul, senators from Montana and Wyoming raised concerns about the White House-backed compromise reached this week.

"This 'compromise bill' would do lasting damage to our nation, to taxpayers and bona fide citizens," said Sen. Craig Thomas, R-Wyo. Thomas is considering several options to alter the bill next week, spokesman Cameron Hardy said.

Sen. Max Baucus, D-Mont., has concerns about the bill upon first glance, his spokesman said. "He's going to take a hard look at the specifics, but at first blush he's not wild about it," said Barrett Kaiser.

The bill could grant legal status to millions of illegal immigrants already in the country who meet certain requirements. It also would boost border security and create an electronic employment verification system. A small bipartisan group of senators hammered out the compromise along with administration officials.

Baucus noted that he has not yet seen the actual language of the compromise plan.

"But I will not support any legislation that does not include strong border enforcement for both the northern and southern borders," Baucus said in a statement. "I do not support amnesty for illegal aliens, and any immigrant who wants to become a citizen must pay back taxes, learn English, and go to the back of the line."

Sen. Jon Tester, D-Mont., also has not seen the final bill language yet, his spokesman Matt McKenna said.

"But what I can tell you is that he wants a policy that is first and foremost fair to the taxpayers," McKenna said. "He does not support amnesty. He believes that we need to strengthen our ports and borders, that folks that want to come to this country need to get in line no different than his ancestors did, and we need to crack down on employers who are knowingly hiring illegals."

Asked whether Tester supports allowing a path to citizenship for illegal immigrants already in the country who meet certain requirements, McKenna said that issue needs to be examined as to what is realistic and practical.

"It's something that he is willing to take a look at through the same lens - is it fair to the taxpayers, does it make sense to homeland security and is it practical," McKenna said.

Thomas and possibly other senators could offer a substitute bill that does not grant what he sees as amnesty, Hardy said. Or he could offer amendments that would either strike the amnesty provisions or make them contingent upon other requirements, such as the Homeland Security Department certifying that the country's borders are secure.

Thomas blasted the compromise as allowing "blanket amnesty," which he said would encourage even more illegal immigration. He also said it would cost the country vast amounts of money in entitlement spending.

"Senate deal-makers have failed to make the necessary changes to enact a strong national immigration policy," he said in a statement. He called the measure poorly crafted.

Thomas's priorities include boosting border security, creating a mandatory electronic employment verification system and supporting tougher employer accountability provisions that increase penalties for those who knowingly hire illegal immigrants.

Sen. Mike Enzi, R-Wyo., said he is still sorting through the proposal but that he would not support amnesty.

"I will not support legislation that rewards illegal immigrants while passing by those who are standing in line, those who are following the rules and trying to enter this country legally," Enzi said in a statement.

Enzi said the "first order of business" is border security and that he may support more resources for that. "We need to know who is coming in and if they aren't coming here legally they should be sent home," he said.

Enzi said the laws must be realistically enforceable and that legal immigrants, mostly seasonal workers, play a vital role in the Wyoming economy.

Enzi said the legislation is still "raw" and its flaws were not exposed because it didn't go through the usual committee process.

The compromise would allow a path to citizenship for millions of immigrants in the country before Jan. 1, 2007.

They first would get a probationary card allowing them to temporarily work in the country legally. After border security and worker identification programs were completed, which is estimated to take about 18 months, they could obtain a "Z visa," putting them on path to citizenship within 12 to 13 years. But heads of households would have to pay fees and a $5,000 fine, pass a background check and an English proficiency test and return to their home country before becoming eligible to apply for citizenship.

The bill would also create a temporary guest worker program. Guest workers could work for two years and then would have to return home for one year before seeking to reenter the country. Total stays would be limited to six years.

That program also could not begin until enforcement provisions are implemented, including boosting the number of border patrol agents to 18,000 and constructing a fence along the Mexican border.

The bill would also revamp future immigration by giving preference to people with employment skills and advanced degrees instead of those with family living legally in the US. It would establish a point system for applicants seeking permanent legal residency on the basis of job skills, education levels, English skills and, lastly, family ties.

An exception would be made for spouses and minor children of U.S. citizens, who would still receive preference.

The House plans to take up immigration legislation in July.