Heading into key debt talks with the White House, congressional Republicans publicly split Thursday over the prospects for their ambitious proposal to transform Medicare.

The division came as two senior Republicans, House Majority Whip Eric Cantor (Va.) and Senate Minority Whip Jon Kyl (Ariz.), entered Blair House Thursday morning for the start of a broad fiscal negotiation with Vice President Biden and Senate Democrats. The talks are designed to reach a deal to allow the Treasury to continue borrowing money to finance the federal government in exchange for budgetary changes that would slash annual deficits.

Less than three weeks after his ambitious 10-year plan was approved, House Budget Committee Chairman Paul Ryan (R-Wis.) said that Republicans are “under no illusion” they will reach an agreement on changes to Medicare and other contentious issues that have divided the two parties in the current budget battle. Rather, he said, House Republicans would accept a deal to raise the legal limit for government borrowing in exchange for spending cuts and other spending controls.

“We are under no illusion that we’re going to get everything we’ve always wanted in this one bill, but let’s get a good down payment,” Ryan said in a question-and-answer session following a Thursday morning speech before the American Council for Capital Formation.

But Boehner told reporters, at a Capitol press conference about two hours later, that he wanted to make clear that entitlements were still an issue heading into the negotiations.

“Let me make this clear: When it comes to increasing the debt limit and the need to have reductions in spending, nothing is off the table except for raising taxes,” Boehner said.

The debate among Republicans came on the first day of negotiations between lawmakers and the White House over reducing the deficit. The initial meeting at Blair House lasted more than two hours and broke shortly after noon. The group plans to meet again Tuesday.

In addition to Cantor and Kyl, the talks involved four congressional Democrats and a host of administration officials, including Biden, Treasury Secretary Timothy Geithner and White House economic adviser Gene Sperling.

As they left the building, Kyl and several other lawmakers pronounced it a good meeting, said they agreed to meet again Tuesday but declined to comment further.

“We made progress. It was a good meeting,” Biden said. “We’re getting the process under way.”

But some Republicans questioned the wisdom of Ryan and Cantor, who made comments similar to Ryan’s in an interview Wednesday.

“It’s not a wise strategy to be taking things off the table today before we’ve begun any discussion to find consensus. I would hope that instead of talking about what’s not on the table we’d be talking about how to find consensus,” Sen. Rob Portman (R-Ohio), a former director of the Office of Management and Budget in the George W. Bush administration, told reporters Thursday.

The dispute is both substantive and symbolic. Ryan and Cantor were voicing the view that it is politically dangerous to set expectations for the debt ceiling talks too high, given the staunch opposition that Obama and Senate Democrats have toward the most far-reaching portions of Ryan’s budget plan.

Passed by the House last month on a party-line vote, Ryan’s plan would shave $4.4 trillion from expected deficits by turning Medicare into a federally funded program giving vouchers to seniors to purchase insurance on the private markets. Medicaid would be transformed into a block-grant program in which governors would have wide latitude to run the health-care program for the poor. And a collection of corporate and upper-income tax cuts would be offset by closing tax loopholes.

Conservatives hailed the Ryan plan as the most ambitious statement of Republican principles in a generation. But it gave Democrats a political opening to accuse the GOP of undermining the extremely popular health-care program for the elderly.

Repeating comments he made the day before, Ryan said Thursday morning that Republicans’ starting point in the negotiations would be the 2012 budget blueprint he wrote, but he acknowledged Republicans might need to look elsewhere to find consensus with Democrats.

“Our starting point is the House budget,” Ryan said. “Now knowing that we are very far apart between the president, the Senate and where we are, we are not under any illusion that we’re going to get some grand slam agreement.”

He added, “Let’s get a single or a double, let’s get a down payment, let’s get some spending cuts, some spending controls as part of this.”

In an interview with The Washington Post Wednesday, Cantor said that the debt limit negotiations would not likely include any significant changes to the “big three” — Medicare, Medicaid or Social Security — and instead could yield more than $700 billion in savings on other mandatory spending programs such as agriculture subsidies. “If we can come to some agreement and act to effect those savings now, this year, it will yield a lot of savings in subsequent years,” he said.

Pressed on that view, Boehner agreed that there needs to be “a recognition of the political realities” but said it was a mistake to pre-emptively take issues out of the negotiating context.

“Nothing is off the table,” he said.

Ryan said he believed a deal on Medicare and other costly entitlement programs would not come until next year, perhaps after the 2012 elections.

“At the end of the day, I think 2012 will make the decision,” he said. “We will give the country a choice of two futures. ... 2012 is going to be the ultimate decider of these things.”

Staff writer Felicia Sonmez also contributed to this story.