WASHINGTON (AP) – The Senate endorsed a chance at citizenship for millions of illegal immigrants Wednesday but also voted to build 370 miles of triple-layered fencing along the Mexican border in increasingly emotional debate over election-year immigration legislation.

Taken together, the votes gave fresh momentum to legislation that closely follows President Bush’s call for a major overhaul of the nation’s troubled immigration system.

The vote was 66-33 against a proposal that would have removed provisions giving an eventual chance at citizenship to illegal immigrants who have been in the country more than two years.

A few minutes earlier, the Senate had voted 83-16 in favor of construction of the fence and 500 miles of vehicle barriers, the first significant victory in two days for conservatives seeking to place their stamp on the measure.

The developments unfolded in a volatile political environment. The White House struggled for a second day to ease the concerns of House Republicans who contend that Bush favors amnesty for illegal immigrants, and demonstrators massed a few blocks from the Capitol demanding immigrant rights.

Construction of the barrier would send “a signal that open-border days are over. … Good fences make good neighbors, fences don’t make bad neighbors,” said Sen. Jeff Sessions, R-Ala. He said border areas where barriers already exist have experienced economic improvement and reduced crime.

“What we have here has become a symbol for the right wing in American politics,” countered Sen. Dick Durbin, D-Ill. He said if the proposal passed, “our relationship with Mexico would come down to a barrier between our two countries.”

The Senate labored to complete work by next week on immigration legislation that generally follows an outline Bush set out in a nationally televised speech this week.

The measure includes provisions to strengthen border security, create a new guest worker program and crack down on the hiring of illegal immigrants.

Most controversially, it offers an eventual chance at citizenship for many of the estimated 11 million to 12 million illegal immigrants already in the country. Senate Republicans staged an impromptu, occasionally emotional debate over whether that amounted to amnesty.

Sen. David Vitter of Louisiana said it did. “Surely this is a pardon from what present law says must happen,” he said of provisions in the bill that require immigrants to undergo background checks, pay back taxes and take other steps before they can become citizens.

Sens. John McCain and Chuck Hagel replied heatedly it was not amnesty.

“Let’s stop the nonsense,” said Hagel, addressing fellow Republicans. “You all know it’s not amnesty.” Said McCain, addressing Vitter, “Call it a banana if you want to … to call the process that we require under this legislation amnesty frankly distorts the debate and it’s an unfair interpretation of it.”

Vitter sought the last word. “Methinks thou dost protest too much.”

The clash erupted after Vitter sought a change in the legislation to strip out provisions of the bill that would allow for guest worker programs and give some illegal immigrants a chance at citizenship.

Supporters of the Senate measure credited Bush’s prime-time Monday night speech with giving fresh momentum to the effort to pass long-stalled legislation.

Across the Capitol in the House, the story was different. Republicans pushed through a border security bill last year, and several members of the rank-and-file have criticized Bush for his proposals. To calm their concerns, the White House dispatched Karl Rove to their weekly closed-door meeting.

Rep. Steve King, R-Iowa, an outspoken opponent of the Senate bill, derided the effort. “I didn’t see it was a persuasive event. If it was about Karl Rove seeking to convince members of Congress after debate that he’s right and we’re wrong it would have been better not to have the meeting,” he said.

King said Rove told lawmakers Bush is sincere about enforcement. But, he added, “The president doesn’t want to enforce immigration law because he’s afraid he’ll inconvenience someone who wants to come into the country for a better life.”

Rep. Peter King, R-N.Y., agreed that Rove did not seem to have been persuasive. “It’s not the kind of issue you can compromise on; either you’re giving amnesty to people who are here illegally or you aren’t.”

At the White House, press secretary Tony Snow defended Bush against criticism. “The president is actually taking a more aggressive role on border security than the House itself took,” he said. “That is the sort of thing that is going to answer a lot of the complaints that we have heard.”

The National Capital Immigration Coalition organized the afternoon demonstration on the National Mall a few blocks from where lawmakers debated the issue they cared about.

“This is a critical moment. We oppose the militarization of the U.S-Mexican border,” said Juan Jose Gutierrez, one of the event’s organizers.