Washington -- Tea Party-backed House Republicans who drove Nancy Pelosi from the speakership last year may inadvertently be handing the San Francisco Democrat significant leverage to protect liberal priorities in the dramatic endgame over raising the $14.3 trillion debt ceiling.

The deal-making now under way involves dueling plans, one by Senate Democrats and one by House Republicans. Any compromise must pass the Republican-controlled House and the Democratic-controlled Senate.

Conservative defections in the House are expected. That would hand Pelosi, the minority leader, a rare opportunity to extract concessions in exchange for delivering the Democratic votes that probably will be needed to avoid a first-ever debt default on Tuesday or a decision to make interest payments to bondholders that would leave other obligations unpaid.

Failure to meet the deadline would also lead to a downgrading of U.S. bonds, which would raise interest rates, damaging the economy and making budget deficits worse by raising the government's borrowing costs.

"Time's going to be short," said Jim Manley, a former top aide to Senate Majority Leader Harry Reid, a Nevada Democrat. Concessions could include such things as an extension of unemployment benefits, as many Bay Area Democrats have demanded. "She will have some leverage," Manley said.

Vote set for today

How much leverage depends on how many conservatives bolt from their leadership on a critical House vote planned for today.

"It all boils down to whether or not the Tea Party folks are going to continue to hold the line," said GOP strategist Ford O'Connell. "Will they stand down and recognize a political victory, or are they going to push it further? And if they push far enough, they could wind up with political suicide."

House Speaker John Boehner, R-Ohio, worked furiously Wednesday to tamp down a rebellion by House conservatives and allied interest groups over his two-step, $3 trillion plan to raise the debt ceiling.

Boehner bluntly told conservative lawmakers to close ranks to avoid a humiliating loss that would deprive Republicans of a plan from which to negotiate with the Senate. Defeat also could open Republicans to a voter backlash if their intransigence is widely seen as the cause of a credit downgrade.

Boehner argued that a reason to support his plan is that "Barack Obama hates it, Harry Reid hates it, Nancy Pelosi hates it." The White House threatened to veto Boehner's plan if it passes, and Reid said not one Senate Democrat would vote for the plan.

GOP leaders also raced to find additional spending cuts to reach a goal of $1.2 trillion in savings for the first debt-ceiling increase (another in six months would be contingent on more savings) after the Congressional Budget Office said the original plan fell far short of that goal.

Embarrassed House leaders had to postpone a vote on their plan Wednesday as they scrambled to find more savings, round up restive conservatives and push back against outside groups urging Republicans to revolt. The budget office confirmed Wednesday that the new Republican bill cuts spending by more than it raises the debt ceiling, meeting a core GOP goal.

The right moment

Pelosi's greatest bargaining power will come in the final negotiations, assuming a compromise emerges in time.

"I don't believe, from what I've seen so far. that anything on a straight party-line vote will make it through or be signed into law," said Rep. Mike Thompson, D-St. Helena.

Earlier in the talks, Pelosi delivered an ultimatum to the White House that Medicare, Medicaid and Social Security be shielded from any cuts to beneficiaries. Those options - along with tax increases that Republicans opposed - have been removed from both plans now on the table and delegated to a super-committee for possible future consideration.

"She's been very clear," said Rep. John Garamendi, D-Walnut Grove (Sacramento County). "Don't touch Medicare, don't touch Social Security, keep your hands off Medicaid."

President Obama's apparent openness to trims in these big entitlement programs generated alarm among Democratic liberals and interest groups.

"That's where Nancy comes in and goes and talks to the president, and tells him, 'You need to know where the Democratic caucus is,' " Garamendi said. " 'If you need caucus votes, don't count on them if these things happen.' "

Working relationship

Pelosi has a good working relationship with Boehner, according to a leadership aide. She has also, as minority leader and as speaker in the last Congress, shown an extraordinary ability to unify Democrats on tough votes, providing added leverage to Senate Democrats and the White House.

Her job was paradoxically made easier by the last election, when the defeat of dozens of moderate and conservative Democrats left her caucus more liberal and less fractious.

A GOP failure to pass Boehner's plan would deal a devastating blow to Republicans by depriving them of a negotiating platform against Senate Democrats and the White House. Even if the bill passes, it becomes only the Republican starting point in negotiations with the Senate and White House on a final compromise that can pass both chambers. The Senate plan is also not expected to pass.

"That is where her greatest bargaining power is," O'Connell said. "Obviously she could be seen as a leader. ... Nancy Pelosi wants to be speaker again, and if she's seen as a victor in this process, holding on to the House is not an absolute for Republicans" in next year's election.