The Treasury secretary must wade into a standoff between Democrats and Republicans over raising the debt limit.WASHINGTON — When Janet L. Yellen was Federal Reserve chair in 2014, she faced a grilling from Republicans about whether the federal government had a plan if the nation’s borrowing limit was breached and measures to keep paying the country’s bills were exhausted.Ms. Yellen, appearing at a congressional hearing, outlined a dire scenario in which financial institutions might try to make payments that they could not cover, because the Treasury Department was out of money, leading to a cascade of bounced checks. She pushed back against the notion held by some Republicans that an economic meltdown could be averted, warning that there was no secret contingency plan.“To the best of my knowledge, there is no written-down plan,” Ms. Yellen said at the time, adding that it was beyond her remit at the Fed. “That’s a matter that is entirely up to the Treasury.”Fending off such a calamity is now squarely the responsibility of Ms. Yellen, who is confronting the biggest test she has faced in her eight months as President Biden’s Treasury secretary. Mr. Biden chose Ms. Yellen to help steer the economy out of the pandemic downturn. But in the face of congressional dysfunction, she has been thrust into a political role, trying to convince reticent Republican lawmakers that their refusal to lift the debt cap — which limits the government’s ability to borrow money — could lead to a financial collapse.It is not a comfortable spot for Ms. Yellen, an economist by training who is now trying to navigate the rough political waters that she tends to avoid by countering legislative gamesmanship with economic logic.Over the past month, Ms. Yellen has reached out to Democrats and top Republican leaders, including Senator Mitch McConnell of Kentucky, the minority leader, and Representative Kevin Brady of Texas, the top Republican on the Ways and Means Committee. She has used those calls to convey the economic risks, warning that the Treasury’s ability to stave off default is limited and that failure to lift or suspend the debt cap by sometime next month would be “catastrophic.”Ms. Yellen has reminded Republicans in the calls that they have been willing to join Democrats in lifting the debt ceiling in the past, and that raising the cap allows the U.S. to pay its existing bills and does not authorize new spending.Thus far, Republicans seem unmoved by Ms. Yellen’s overtures.In a call with Ms. Yellen last week, Mr. Brady said he told the secretary that he would be happy to work with her on a bipartisan framework focused on financial stability and curbing government spending but, barring that, Democrats should not expect Republicans to help them address the debt limit.“They are playing a dangerous political game with our economy and it’s absolutely unnecessary,” Mr. Brady said on Wednesday.Mr. McConnell conveyed a similar message during a telephone conversation with Ms. Yellen last week, his spokesman said. Mr. McConnell’s former chief of staff, Brian McGuire, said the Kentucky Republican would not be persuaded by pressure tactics and suggested that the Treasury secretary should direct her economic warnings at Democrats.“If I were advising Secretary Yellen, I’d suggest she be highly skeptical of the Democratic strategy on the debt limit,” said Mr. McGuire, who was Treasury’s assistant secretary for legislative affairs from 2019 to 2020.On Thursday, Ms. Yellen appeared at a news conference with Speaker Nancy Pelosi of California and Senator Chuck Schumer of New York, the majority leader. Ms. Pelosi assailed Republicans for refusing to join Democrats in covering costs that both parties have incurred, including the $1.5 trillion tax cuts that Republicans passed during the Trump administration.“This is a credit-card bill that we owe,” Ms. Pelosi said.Democrats wanted to pair the federal debt limit increase with legislation to keep the government funded through early December, which would require Republican support in the Senate. With no such agreement in sight, the White House’s Office of Management and Budget on Thursday alerted federal agencies to review their shutdown plans, given funding is scheduled to lapse next week.Democrats do have another legislative option for raising the borrowing cap — they could pair it with the $3.5 trillion spending bill that they are aiming to pass along party lines using a fast-track process known as budget reconciliation. However, that would impose procedural hurdles they are trying to avoid, and Democrats have yet to agree on what the spending bill should include or how to pay for it. Party leaders claimed progress toward a deal on Thursday, saying they had agreed upon an array of possible ways to pay for it. But they offered no details about what programs would be included or what the total cost would eventually be, and what they called a “framework agreement” appeared to be modest.With the debt limit increase becoming so contentious, Ms. Pelosi signaled for the first time on Thursday that Democrats could ultimately strip it from the government funding bill because of Republican opposition.“We will keep our government open by Sept. 30, which is our date, and continue the conversation about the debt ceiling, but not for long,” she said.Ms. Yellen, who has kept a low public profile in the last month, did not make a statement at the news conference and took no questions.In private, she has tried to amp up the pressure. Ms. Yellen has personally warned the chief executives of the nation’s largest banks and financial institutions about the very real risk of default. Over the past several days she has spoken to Jamie Dimon of JPMorgan Chase, David M. Solomon of Goldman Sachs, Brian T. Moynihan of Bank of America and Laurence D. Fink of BlackRock, telling them about the disastrous impact a default would have, according to people familiar with the calls.The banking industry traditionally wields significant influence with Republicans; the biggest financial services lobbying groups wrote a letter to top lawmakers earlier this month urging them to take action.“Any default would negatively impact the general economy, disrupt the operations of our financial markets, undermine confidence, and raise funding costs in the future,” they wrote.Ms. Yellen has also sought the counsel of her predecessors, including Steven T. Mnuchin, Jacob J. Lew, Timothy F. Geithner and Henry M. Paulson. Mr. Paulson, who served under President George W. Bush and maintains strong ties with Republican lawmakers, has echoed Ms. Yellen’s concerns about the impact of a default in conversations with Mr. McConnell, according to a person familiar with the matter.Earlier this week, six former Treasury secretaries sent a letter to top lawmakers, warning that a default would blunt economic growth, roil financial markets and sap confidence in the United States.“Failing to address the debt limit, and allowing an unprecedented default, could cause serious economic and national security harm,” they wrote in the letter that was published by Ms. Yellen’s Treasury Department.Ms. Yellen’s task has been complicated by the fact that while she can readily convey the economic risks of default, the debt limit has become wrapped up in a larger partisan battle over Mr. Biden’s entire agenda, including the $3.5 trillion spending bill.Republicans, including Mr. McConnell, have insisted that if Democrats want to pass a big spending bill, then they should bear responsibility for raising the borrowing limit. Democrats call that position nonsense, noting that the debt limit needs to be raised because of spending that lawmakers, including Republicans, have already approved.“This seems to be some sort of high-stakes partisan poker on Capitol Hill, and that’s not what her background is,” said David Wessel, a senior economic fellow at the Brookings Institution who worked with Ms. Yellen at Brookings.While lawmakers squabble on Capitol Hill, Ms. Yellen’s team at Treasury has been trying to buy as much time as possible. After a two-year suspension of the statutory debt limit expired at the end of July, Ms. Yellen has been employing an array of fiscal accounting tools known as “extraordinary measures” to stave off a default.Uncertainty over the debt limit has yet to spook markets, but Ms. Yellen is receiving briefings multiple times a week by career staff on the state of the nation’s finances. They are keeping her informed about the use of extraordinary measures, such as suspending investments of the Exchange Stabilization Fund and suspending the issuing of new securities for the Civil Service Retirement and Disability Fund, and carefully reviewing Treasury’s cash balance. Because corporate tax receipts are coming in stronger than expected, the debt limit might not be breached until mid- to late October, Ms. Yellen has told lawmakers.A Treasury spokeswoman said that Ms. Yellen is not considering fallback plans such as prioritizing debt payments if Congress fails to act, explaining that the only way for the government to address the debt ceiling is for lawmakers to raise or suspend the limit. However, she has reviewed some of the ideas that were developed by Treasury during the debt limit standoff of 2011, when partisan brinkmanship brought the nation to the cusp of default.A new report from the Bipartisan Policy Center underscored the fact that if Congress fails to address the debt limit, Ms. Yellen will be left with no good options. If the true deadline is Oct. 15, for example, the Treasury Department would be approximately $265 billion short of paying all of its bills through mid-November. About 40 percent of the funds that are owed would go unpaid.“Realistically, on a day-to-day basis, fulfilling all payments for important and popular programs would quickly become impossible,” the report said, pointing to Social Security, Medicare, Medicaid, defense, and military active duty pay.Tony Fratto, a Treasury official during the Bush administration, lamented that Ms. Yellen is operating without any leverage. Democrats, he said, appeared to have miscalculated when they thought that Republicans would be too ashamed to block a debt limit vote after supporting a suspension of the borrowing cap when President Donald J. Trump was in office.“I think that was in the ‘hope’ category,” Mr. Fratto said. “This is Washington in 2021 — your hopes will be dashed.”Lananh Nguyen More