Business leaders and former government officials urged Congress’s deficit-reduction supercommittee to cut more than the $1.5 trillion in long-term savings it is assigned to find.

“We urge you to ‘go big’ and develop a large-scale debt reduction package sufficient to stabilize the debt as a share of the economy,” they said in a letter today to the panel. The group is led by the co-chairmen of President Barack Obama’s 2010 fiscal commission, Erskine Bowles and Alan Simpson.

The 12-member, bipartisan supercommittee is scheduled to hold its first hearing tomorrow.

About 60 people signed the letter. Among them are Roger Altman, founder and chairman of Evercore Partners; Peter Davis, president of Davis Capital Investment Ideas; and former senators Judd Gregg, a New Hampshire Republican, and Bob Kerrey, a Nebraska Democrat.

The supercommittee’s savings goal “is peanuts, as we used to say in the grandstand,” Simpson, a Republican former senator from Wyoming, said at a news conference today. “They’re going to have to go for more than that.”

President Barack Obama is asking Congress to approve his $447 billion plan to create jobs through tax cuts and new spending, proposing it be paid for with tax increases that could be folded into the supercommittee’s jurisdiction.

‘Real Deficit Reduction’

Bowles said the U.S. needs to achieve about $4 trillion of “real deficit reduction” over the next decade.

“We need to do this to reassure the markets,” said Bowles, who was chief of staff for former President Bill Clinton. He and Simpson appeared with Maya MacGuineas, president of the Committee for a Responsible Federal Budget, which organized the letter.

White House spokesman Jay Carney said in a briefing today that the supercommittee should “overachieve,” declining to say specifically by how much the committee’s mandate should be expanded. Obama outlined his jobs plan in a speech to Congress last week.

In his address, Obama also signaled a willingness to negotiate on the most important areas for Republicans, overhauls to Medicare and Medicaid. So far Republicans have rejected the idea of increasing the committee’s savings target, which would increase pressure to also adopt tax increases to meet the new goal.

‘Nearly Impossible’

Following Obama’s speech, the Republican supercommittee co-chairman, Representative Jeb Hensarling of Texas, said any plan to increase its savings mandate would hamstring the panel. “This proposal would make the already-arduous challenge of finding bipartisan agreement on deficit reduction nearly impossible,” Hensarling said.

Simpson warned Republicans that all proposals to cut the debt, including entitlement cuts and new revenue, need to be on the table. “The heat is on,” he said.

Bowles said he’s optimistic after speaking privately with several supercommittee members, including Republicans, that the committee can increase its target and discuss revenue. “The members I’ve talked to have been very clear that everything’s on the table,” said Bowles.

“The politics have changed quite a bit since December of last year,” Bowles said. That’s when he and Simpson failed to get enough support from the Obama panel members to send their recommendation for a $3.8 trillion budget-cutting plan for a vote in Congress. The plan included tax increases as well as spending cuts.

According to the Committee for a Responsible Federal Budget, even if the supercommittee reaches agreement on $1.5 trillion in deficit reduction, that won’t arrest the debt’s exponential growth. Debt as a percentage of gross domestic product would still increase from 67 percent this year to more than 75 percent by 2021, according to the committee’s estimates, and it would take $3 trillion in deficit reduction to bring the debt below 70 percent of GDP by 2021.