House Minority Leader Nancy Pelosi, D-Calif., said Tuesday that she backs President Barack Obama's newest proposal to avert the fiscal cliff, defying some progressive Democrats who object to an included cost-of-living calculation that could effectively cut entitlement benefits to Social Security recipients.

Asked by NBC's Andrea Mitchell if she believes she can rally enough Democratic support to pass the White House's plan, Pelosi responded "Yes, I do."

"I believe the president has demonstrated great leadership in what he put forth," she said, arguing that the White House plan would help avert the cliff, create consumer confidence and avoid a credit rating downgrade.

Pelosi pushed back on progressive opponents of one compromise measure that would modify the way cost-of-living increases are calculated to determine Society Security payments. While some in the Democratic Party say that the change -- called "chained CPI" --  would effectively cut Social Security payments, the minority leader said Tuesday that the effects on poor recipients would be minimal once all of the specifics of the deal are worked out.

"The details of this are not all ironed out, but they all mitigate for helping the poorest and neediest in our society, whether they are [Supplemental Security Income] recipients, whether they're 80 and older, or whether they're truly needy," she said.

But, she added, she would join some of those progressive Democrats in opposing an increase in the Medicare eligibility age.

Kevin Lamarque / Reuters

U.S. House Minority Leader Nancy Pelosi speaks to reporters in the Capitol in Washington December 13, 2012.

Pelosi also came out against House Speaker John Boehner's "Plan B" proposal earlier Tuesday to push a standalone measure that would address tax rates for earners under $1 million.

"Plan B, I would call it 'Plan Befuddled," she said of Boehner's suggestion, adding that the measure cannot pass both houses of Congress.

'It's a tactic, but it's not a serious proposal," she said.

Republicans have pointed out that Pelosi herself suggested in May that tax rates should be maintained for all earners under $1 million, the same threshold that Boehner offered today.

Pelosi said Tuesday that her own proposal was in part a way to "smoke out" the opposition in getting Republicans to agree to at least some rate hikes, a move that they have now made in -- Pelosi argues -- a victory for the president.

"I'm glad he's taking up some of my suggestions," she said of Boehner. 'My next suggestion would be to put something on the table - as we were suggesting then to smoke out the Republicans - at what level would you raise the rates on the wealthiest people in this country? Not 'would you raise them at a million dollars?' That was the point of that exercise."

U.N. Ambassador Susan Rice rejected calls to arm the Syrian rebels on MSNBC's Andrea Mitchell Reports, arguing that would further inflame the region into a proxy war -- and that the Syrian opposition are not a united force.

Rice's comments came right after a Security Council briefing from former U.N. Secretary General Kofi Annan's team in Geneva, after their departure from Damascus.

Rice also accused Iran of aiding the regime's militias -- and talked about Russia's role.

"We think Iran is actively supporting its longtime ally Assad and providing material and other support," Rice said, "and indeed they said so publicly, in a statement on their own website. They bragged about their engagement in Syria and that is one of the reasons among others - they're not the only ones that are supporting the Syrian regime - that this is a conflict of a different character, with much broader regional implications should it continue to spin out of control."

Rice also said the U.S. continues to lobby Russia and noted its potentially pivotal role.

"We think the Russians have the greatest stake, in fact, in ensuring that the Syrian regime meets its obligations under the Annan plan, so that we're not having to resort to sanctions or having to see the region engulfed in a wider conflict," Rice said. "And that's the message that we're conveying to the Russians. It is their interest and indeed their responsibility as the Syrian government's best friend on the Security Council to put maximum pressure on the Syrian government to adhere to the commitments it's made. And that is why it's time that we start talking about this problem and thinking about this problem in these stark terms."

She added, "I think they are beginning to look at this situation with the kind of clarity it deserves, and recognizing that if they want to preserve Kofi Annan's mission - its opportunity to provide a peaceful political solution, which is what they say they do - either they're going to have to move Assad to a very different place than he's been in thus far, or join with us and others in maximizing Security Council pressure on the regime."

Here's a partial transcript:

AVOIDING A "PROXY WAR"

ANDREA MITCHELL: What has to happen on the ground for the administration to decide that there needs to be weapons and material support to the opposition?

RICE: Our view has been that the best way to resolve this is not by intensifying the militarization, not by providing further arms into what is already a hot conflict - but to try to resolve it through non-military means, through a diplomatic and political process. Now as I said that may prove ultimately not to be possible. We haven't reached that point yet - and for this to become a proxy war with countries all over the region and beyond funneling weapons in there is basically conceding a massive fire burning in that region. For those who are advocating arming the opposition, they really ought to consider the consequences of that approach and also to ask, frankly, who are they arming inside of the Syrian opposition. You know and we know, it's not a unified opposition. It's fragmented. They don't have common command and control. There are some extremist elements mixed in there, and we know much less about the intentions of the Syrian opposition than we did even of the Libyan opposition at the time. And I want to remind you that we did not arm the Libyan opposition.

RE IRAN BRAGGING ABOUT HELPING REGIME FORCES:
AM: Let me ask you about some of these outside forces. What is the role of Iran in all of this?

SR: We think Iran is actively supporting its longtime ally Assad and providing material and other support - and indeed they said so publicly, in a statement on their own website. They bragged about their engagement in Syria and that is one of the reasons among others - they're not the only ones that are supporting the Syrian regime - that this is a conflict of a different character, with much broader regional implications should it continue to spin out of control.

RUSSIA'S ROLE

AM: And what makes us think that Vladimir Putin, who wouldn't even come to the NATO Summit meeting, and has shown no friendliness toward the Obama administration - what makes us think that Vladimir Putin is now going to be helpful in pressuring his political ally Assad to give up power?

RICE: Let's be clear. The relationship broadly speaking between the United States and Russia over the course of the last several years is much improved over the past. There are areas in which we have real differences, but this improvement - this reset as we call it - has occurred with Vladimir Putin with prime minister - and we expect it will continue. But on this issue we disagree and we are continuing to talk with the Russians and pressure them. We'd like to see them make a voluntary decision to stop providing military support - even of prior agreed contracts to the Syrian regime. We think the Russians have the greatest stake in fact in ensuring that the Syrian regime meets its obligations under the Annan plan so that we're not having to resort to sanctions or having to see the region engulfed in a wider conflict. And that's the message that we're conveying to the Russians. It is their interest and indeed their responsibility as the Syrian government's best friend on the Security Council to put maximum pressure on the Syrian government to adhere to the commitments it's made. And that is why it's time that we start talking about this problem and thinking about this problem in these stark terms...

AM: Did you see any flexibility on Russia's part in the meeting today? 

SR: We'll see where the Russians end up. I think they are beginning to look at this situation with the kind of clarity it deserves, and recognizing that if they want to preserve Kofi Annan's mission - its opportunity to provide a peaceful political solution, which is what they say they do - either they're going to have to move Assad to a very different place than he's been in thus far, or join with us and others in maximizing Security Council pressure on the regime.