Senate Democratic leaders are attempting a balancing act on Medicare — by showing openness to containing the program’s ballooning costs but still drawing the line at cutting benefits.

The gambit is aimed at convincing voters that Democrats take the need to reduce the deficit seriously but will protect seniors more than Republicans — a message Democratic leaders think will help them retain their Senate majority against tough odds in 2012.

In a move that appears designed for media consumption, five Democratic Senators up for re-election in 2012 sent a letter Monday to Vice President Joseph Biden asking him to hold firm against cutting benefits for seniors and to reject the House-passed proposal to transform Medicare during his bipartisan negotiations to increase the $14.3 trillion debt limit.

“For the good of the nation’s seniors, [the House plan] must remain off the table,” the Senators wrote.

But in a follow-up conference call with reporters, Senate Democratic Conference Vice Chairman Charles Schumer left open the possibility of reaching a deal that would include trimming Medicare.

“That will be up to the negotiators,” the New York Democrat said. He was careful to note, however, that a deal including Medicare is possible “as long as it doesn’t reduce benefits to the beneficiary.”

In-cycle Sens. Sherrod Brown (Ohio), Benjamin Cardin (Md.), Claire McCaskill (Mo.), Bill Nelson (Fla.) and Jon Tester (Mont.) signed the letter to Biden.

“Our nation’s seniors are not responsible for the fiscal challenges we face, and they should not be responsible for shouldering the burden of reducing our deficits,” they wrote.

McCaskill’s signature on the letter is notable, given that she has been among the most hawkish of Democrats on the need to cut the growth of spending on Medicare and Social Security in order to save the programs for the future.

She is the principal Democratic co-sponsor of a proposal that would require across-the-board cuts to federal spending — including Social Security and Medicare benefits — unless Congress cuts the overall level of spending to 20.6 percent of the gross domestic product in the next decade. That proposal has come under heavy fire from the left and from seniors’ groups such as AARP, as well as from some of her fellow Democrats. At the press conference announcing that bill, McCaskill said they need to be reformed, and she endorsed means testing.

“Will I fight like a tiger to make sure that we protect Social Security? I absolutely will. But should we be buying prescription drugs for [billionaire businessman] Warren Buffett with federal tax dollars? Well, that’s just nuts!” she said then.

“She is trying to carve out a middle ground there,” said a Senate Democratic aide, noting that while she has supported some ways to reduce waste, “she does not support a dismantling of the Medicare system like the [House] plan.”

Senate Minority Leader Mitch McConnell (R-Ky.) last month demanded Medicare cuts in return for his support for any debt ceiling increase.

Schumer offered as an example cuts in payments to drugmakers as one way to save $100 billion or more, as well as building on last year’s health care overhaul to pay providers based on outcomes.

But Schumer challenged the GOP to give up on the House Republican budget blueprint, which aims to replace traditional Medicare with a subsidy to buy private insurance. It would apply only to future beneficiaries, but it was defeated on the Senate floor before the recess.

“Republicans won’t give up on the House-passed plan to eliminate Medicare as we know it. … If Sen. McConnell has other plans in mind, we should hear it,” Schumer said.

McConnell, for his part, ripped Democrats for focusing on the election instead of coming up with a specific proposal or budget of their own.

“They have no plan, no proposals, no sense of urgency,” McConnell said on the Senate floor. “They run the White House and they run the Senate, and yet their entire approach is to sit back and wait. … Just wait for the next election. Let Republicans offer solutions, and then we’ll attack them and pretend you care about jobs.”

McConnell spokesman Don Stewart praised Schumer for being open to Medicare savings.

“Looks like Sen. Schumer is joining the bipartisan chorus that wants Medicare reform as part of the deficit reduction talks,” he said. “I’m not sure how he squares that with his party’s campaign ads, but this is certainly encouraging. Maybe next, Democrats will actually offer a budget ­— or at least a plan. But this is progress.”

But Democrats pushed back against that notion. “Republicans will be forced to either join us in taking on the big insurance and drug companies and thus admit that the reforms we made to Medicare in the health care law were the right thing to do all along, or else they can continue to stand by the [House] plan,” one senior Senate Democratic aide said.

Schumer and other Senators on the conference call — including Brown and Cardin — repeated that the House proposal to overhaul Medicare and transform it into a subsidy for insurance could not pass.

“The Republicans who are negotiating on the debt ceiling are trying to use it to advance their extreme agenda,” Brown said. Brown went further than Schumer, saying Medicare should be off the table entirely as part of the debt ceiling talks and should be dealt with separately.

“Let’s take Medicare totally off the table now,” Brown said.