WASHINGTON (AP) — Attention is shifting to the House and its conservative majority after the Senate passed a landmark immigration bill opening the door to U.S. citizenship to millions while pouring billions of dollars into securing the border with Mexico.

The bill's prospects are highly uncertain in the Republican-led House, where conservatives generally oppose citizenship for immigrants living in the country unlawfully. Many also prefer a step-by-step approach rather than a comprehensive bill like the legislation the Senate passed Thursday on a bipartisan vote of 68-32.

Following the Senate vote, President Barack Obama, who's made an immigration overhaul a top second-term priority, called on the House to act.

"Today, the Senate did its job. It's now up to the House to do the same," Obama said in a statement issued as he traveled in Africa. "As this process moves forward, I urge everyone who cares about this issue to keep a watchful eye. Now is the time when opponents will try their hardest to pull this bipartisan effort apart so they can stop common-sense reform from becoming a reality. We cannot let that happen."

Members of the Senate's so-called Gang of Eight, the senators who drafted the bill and hoped a resounding vote total would pressure the House, echoed the plea.

"To our friends in the House, we ask for your consideration and we stand ready to sit down and negotiate with you," Sen. John McCain, R-Ariz., said. "You may have different views on different aspects of this issue, but all of us share the same goal, and that is to take 11 million people out of the shadows, secure our borders and make sure that this is the nation of opportunity and freedom."

At a news conference, House Speaker John Boehner, R-Ohio, made clear the House would not simply take up the Senate bill as some Democrats and outside advocates are calling for, but would chart its own legislation with a focus on border security. How exactly Boehner will proceed remained unclear, but the speaker has called a special meeting of his majority Republicans for July 10 to go over options.

"The House is not going to take up and vote on whatever the Senate passes. We're going to do our own bill," Boehner said. "It'll be legislation that reflects the will of our majority and the will of the American people."

The bill passed by the Senate devotes $46 billion to border security improvements, including calling for a doubling of the border patrol stationed on the U.S.-Mexico border and the completion of 700 miles of fencing — changes added at the last minute to attract Republican support. No one would be able to get a permanent resident green card until those border enhancements and others were in place.

The bill also makes it mandatory for employers to check their workers' legal status, sets up new visa programs to allow workers into the country and establishes new tracking systems at seaports and airports to keep better tabs on people entering and leaving the country.

At its contentious core, though, is a 13-year path to citizenship for the 11 million immigrants living in this country illegally.

Without such a provision, senators say the legislation could not pass the Senate. With it, its prospects are difficult in the House.

Sen. Chuck Schumer, D-N.Y., predicted that the House might end up having to pass the Senate bill after failing to find any other avenue forward and feeling pressure from the public to act.

But that approach is strongly opposed by many conservatives. Boehner also dismissed the idea of relying on Democratic votes instead of a majority of his Republicans to pass an immigration bill.

At the same time Boehner said he hopes the bill will be bipartisan, and he encouraged a House group of four Democrats and three Republicans trying to forge a compromise to continue their efforts.

He offered no details on how a House bill could be both bipartisan and supported by more than half of his own rank and file, given that most of the single-issue immigration bills that have moved through the House Judiciary Committee recently did so on party-line votes over the protests of Democrats. None envisions legal status for immigrants now here illegally.

Boehner declined to say whether there were circumstances under which he could support a pathway to citizenship, but he made clear that securing the border was a priority.

"People have to have confidence that the border is secure before anything else is really going to work. Otherwise, we repeat the mistakes of 1986," he said, referring to the last time Congress overhauled the immigration system.

One option could be to bring up one or more of four narrowly focused immigration bills approved by the Judiciary Committee this week and last, hoping to pass it and use it as a vehicle for House members to enter into negotiations with senators on a merged bill in the fall or winter.