WASHINGTON -- Election-year concerns and presidential jockeying are dominating the congressional debate over President Bush's immigration plan, threatening to scuttle the chances of an overhaul this year.
The issue, which has exposed deep divisions among Republicans, will spark a showdown next week in the Senate, with separate plans offered by three GOP senators, each of whom is exploring a presidential run in 2008.
Any Senate compromise measure would face long odds in the more conservative House, which has passed a tough border security measure and is hostile to the White House proposal for a guest worker program that would allow the approximately 12 million illegal immigrants in the United States a chance at citizenship.
The topic is a notoriously difficult and emotional one riddled with risks for lawmakers, touching on voters' post-9/11 security concerns and job worries as it threatens to devolve into a stalemate with undertones of protectionism and xenophobia.
Bush alluded to the risk of a "fractious debate" during a news conference Tuesday, saying the discussions, "if not conducted properly, will send signals that I don't think will befit the nation's history and traditions."
The Senate debate pits Majority Leader Bill Frist of Tennessee, who is offering a tough plan to crack down on illegal immigration and fortify the nation's borders, against Arizona Sen. John McCain, who is pushing a guest worker program like one Bush has proposed and which appeals to businesses that depend on immigrants' labor.
Sen. Chuck Hagel of Nebraska has also waded into the fight with a proposal to allow some immigrants to pay fines and apply for legal status.
All three are contemplating presidential runs, and their struggle over immigration mirrors a broader dispute among the White House, Republican lawmakers and strategists over how best to appeal to voters on the issue during a hard-fought election year.
Some strategists think the party should take a hard-line stance that plays to Republicans' traditional advantage on security issues, emphasizing - as Frist's measure does - border control and steep penalties for illegal immigrants and those who hire them.
Such an approach appeals to the party's conservative base, which has a strong hand in deciding the Republican presidential nominee.
Others side with Bush, who has advocated a more permissive, pro-business approach that pairs stiffer border security with a new plan to allow people to come to the country to work and give those here illegally a chance to become citizens.
His stance - derided by conservatives as amnesty for lawbreakers - echoes the "compassionate conservative" theme on which Bush first ran for president, and some strategists believe it can be a winning approach for Republicans.
"My only advice for the Congress and for people in the debate is understand what made America. We're a land of immigrants," Bush said last week in Cleveland. "We've got to treat people fairly. We've got to have a system of law that is respectful for people."
The chances of passing an immigration overhaul could crumble under the weight of dueling presidential ambitions and election-year worries. Still, the debate will give Republicans seeking re-election this year a chance to shape their messages and cast key votes on immigration. And for those considering presidential bids, it offers a chance to test their arguments on the subject.
Frist and McCain are using contrasting strategies in trying to gain the advantage in the immigration debate, said Tamar Jacoby, an analyst at the conservative Manhattan Institute.
Frist is gambling that Republican primary voters will reward him for a tough approach, she said, and McCain is betting that the party faithful would prefer a plan that can address the vexing issue of what to do with the immigrants already here.
"Frist is thinking that the answer is crack down, and that's what the public will like, and McCain is saying solve it, and that's what the public is looking for," Jacoby said.
"Nobody's there yet. This is still no-man's land."
A groundswell of pressure for immigration changes has swept the nation in recent months, transforming the issue from an intense but parochial area of concern among residents of border states to one that worries a broad swath of voters who live nowhere near a checkpoint, including those in Maryland.
There is widespread support for addressing immigration problems, including among Republicans, according to public polls. An ABC poll in January found that 57 percent of those questioned disapproved of the way Bush was handling the issue, and an NBC News/Wall Street Journal poll this month found that 71 percent would be more likely to support a candidate who favored tighter controls on illegal immigration.
But there is little consensus over the thorny question at the center of this week's debate: what to do with the throngs of illegal immigrants already here, many of them working and raising families.