The Senate opened debate on an election-year immigration bill Wednesday, and leading Republicans swiftly clashed over whether the legislation would amount to amnesty for millions of illegal residents in the United States.

The legislation "goes too far in granting illegal immigrants with what most Americans will see as amnesty," said Senate Majority Leader Bill Frist of Tennessee, the first to speak on the bill. "I disagree with this approach ... because granting amnesty now will only encourage further and further disrespect for the law."

Moments later, the chairman of the Senate Judiciary Committee, Sen. Arlen Specter of Pennsylvania, bluntly rebutted his fellow Republican. "I want to disagree with him head on. It is not amnesty," he said. Specter said illegal residents would have to be current on their taxes, undergo background checks and clear other obstacles before gaining a place on a "citizenship track."

The disagreement underscored not only the divisions within the Senate, but the extent to which the fate of 11 million illegal immigrants has come to dominate the issue. Adding a fresh layer of political complexity, Hispanics make up a fast-growing segment of the electorate and have demonstrated by the hundreds of thousands in recent days in opposition to punitive legislation.

In general, the bill under consideration in the Senate is designed to strengthen enforcement of U.S. borders, regulate the flow into the country of so-called guest workers and determine the legal future of the illegal population scattered across all 50 states.

The House has passed legislation limited to border enforcement. Republican leaders have signaled in recent days they are receptive to an expanded measure, and immigration has taken on added importance for the GOP in the run-up to midterm elections.

"We are not going to discount anything right now," House Speaker Dennis Hastert said several hours before the Senate debate opened. "Our first priority is to protect the borders. We also know there is a need in some sectors of this economy for a guest worker program," added the Illinois Republican.

President Bush has urged Congress to approve legislation that strengthens border security and contains enforcement at the workplace and a temporary guest worker program.

"There are people doing jobs Americans will not do," Bush told reporters Wednesday. "Many people who have come into our country are helping our economy grow. That's just a fact of life."

Specter shepherded legislation through the Judiciary Committee on Monday on a vote of 12-6. The outcome was unusual in the Republican-controlled Senate since there were more GOP committee members against the measure than voting in favor.

The Pennsylvania Republican said at the time he would continue to seek agreement on changes, and he repeated his remarks on the Senate floor. "If there is a better way to bring these 11 million people forward so that we can identify them, we are open to any suggestions which anyone may have," he said.

Frist and Specter were not the only lawmakers to address the issue of amnesty, an emotionally charged label that political candidates all hope to avoid.

Sen. Patrick Leahy of Vermont, the senior Democrat on the Judiciary Committee, sided with the panel's chairman. "Opponents of a fair, comprehensive approach are quick to claim that anything but the most punitive provisions are amnesty. They are wrong," he said.

But Sen. Jeff Sessions, R-Alabama, was quick to counter. "The truth is this bill is amnesty," he said, adding that if others insist on saying otherwise, "we'll keep talking about it every day this week."

The legislation that cleared committee would double the Border Patrol and allow for a virtual wall of unmanned vehicles, cameras and sensors to monitor the U.S.-Mexico border. It also calls for detention facilities for an additional 10,000 immigrants who may face deportation.

The committee voted down proposed criminal penalties on immigrants found to be in the country illegally.

The bill would establish a temporary program for up to 1.5 million farm workers who are in the country illegally, giving them an opportunity to achieve legal status.

Separately, it creates a new guest worker program for would-be immigrants, allowing them to enter the country under a three-year visa, renewable for another three years, then apply for legal permanent residence without leaving the United States. The program would initially be open to 400,000 individuals a year, a figure to be adjusted annually based on the labor market.