Mr. Biden, 77, has told associates that he considers his two terms as vice president and his knowledge of how a White House operates from the inside as crucial advantages in building out a government. And he has made it plain in public and private that a diverse team is central to his mission.“Men, women, gay, straight, center, across the board, Black, white, Asian,” Mr. Biden said this spring when talking about his prospective cabinet. “It really matters that you look like the country, because everyone brings a slightly different perspective.”Though Mr. Biden and Democrats had aggressively pushed to take control of the Senate, the party fell short in hotly contested races this week. Now Senate Republicans are likely to hold veto power over his most senior appointments, a reality that looms large over conversations, even if Democrats could still conceivably control the Senate if they win two runoff elections in Georgia in January. Lael Brainard, who sits on the Federal Reserve’s board of governors and served in the Treasury Department under Mr. Obama, is the most talked-about candidate to run the department, especially if the Senate is controlled by Republicans, which would make it harder to confirm a more progressive choice like Senator Elizabeth Warren of Massachusetts. Mr. Biden’s team quietly began raising money for his transition operation in May and has raised at least $7 million to pay for its efforts. The Biden camp has prepared for multiple scenarios in case Mr. Trump refused to concede and his administration would not participate in a transition.- Advertisement – So far, officials in Mr. Trump’s government have worked in good faith, according to Biden officials, who said they hoped and expected that cooperation to continue.As coronavirus infections hit new highs, Mr. Biden’s aides are planning for the first critical transition decisions to focus on health care and addressing the pandemic, the central theme of his campaign in the final months. They have assembled an internal group of roughly two dozen health policy and technology experts to look at the development and delivery of a vaccine, improving health data and securing supply chains, among other issues.Among those expected to play a key health care role in a Biden administration is Vivek Murthy, a former surgeon general under President Barack Obama, who has privately advised Mr. Biden for months on the pandemic and is expected to play a large public role as a face of the potential Democratic administration’s response to the virus, dispensing advice on mask-wearing and social distancing.- Advertisement – Like Mr. Biden, Mr. Kaufman is seen as an institutionalist, and he in fact wrote the law devoting additional government resources to transition teams. Yohannes Abraham, who worked in the Obama White House as a top aide to Valerie Jarrett and the National Economic Council, is overseeing the day-to-day operation.Given his decades-long career in Washington, Mr. Biden has numerous relationships from his time in the Senate and the White House with people across various policy areas. That history also means that his transition team has faced a crush of outside advice and former Biden associates jockeying for jobs and influence.Parts of the cast that had Mr. Biden’s ear throughout the presidential campaign — Anita Dunn, a senior adviser; Steve Ricchetti, another former vice-presidential chief of staff; and Mr. Klain — are among those guiding the formation of a would-be government. Senator Kamala Harris of California, his running mate, is generating names and speaks regularly to Mr. Biden. In Mr. Biden’s policy orbit on the campaign, Jake Sullivan and Antony J. Blinken are widely seen as the most influential figures, and both are expected to hold senior posts in a potential administration. Even before it was clear that Democrats would not win a clear majority in the Senate, Mr. Biden’s advisers began gearing up for bruising cabinet confirmation battles, bringing in top Obama veterans to run what is informally being called a transition war room. If Mr. Biden wins, he is expected to initially focus on filling top posts at the White House, including chief of staff, the most powerful single staff position. Ron Klain, his former chief of staff as vice president, who served as the White House Ebola response coordinator under Mr. Obama, is seen to have the inside track for that job, though others are still reportedly under serious consideration.At the center of Mr. Biden’s transition planning is Ted Kaufman, his former chief of staff in the Senate, who was appointed to replace Mr. Biden as a senator after he became vice president, as well as Jeff Zients, a former Obama administration official. The behind-the-scenes activity underscored that even as Mr. Biden publicly offered a disciplined message about counting every vote and refrained from claiming victory, he was already mapping out a quick start in office as the nation faces a worsening pandemic and a damaged economy.Mr. Biden, who ran from Day 1 on a message of bringing the country together, is said to be interested in making a bipartisan gesture as he plans a prospective government after a divisive election whose results President Trump has tried to undermine. Mr. Biden is looking to fill out his possible White House staff first, with cabinet posts not expected to be announced until around Thanksgiving, according to more than a half-dozen people familiar with the planning process who spoke on the condition of anonymity to discuss the transition. Some Democratic House members who endorsed Mr. Biden early, such as Representative Filemon B. Vela Jr. of Texas and Representative Brendan Boyle of Pennsylvania, could be in line for administration positions if they wanted them.“We have an expression where I come from: You never forget those who brung you to the dance,” Mr. Biden said at a stop with Mr. Boyle in Philadelphia this week.The Biden operation is preparing for Mr. Trump to potentially put up transition roadblocks. The transition team has already assembled a staff of more than 75 officials, with plans for that number to balloon to roughly 300 transition staff members by Inauguration Day in January. The administrator for the General Services Administration has the legal authority to release about $6.6 million in federal funding to Mr. Biden’s transition, and in past years has done that soon after the race is called.Pamela Pennington, a spokeswoman for the G.S.A., said in a statement that Emily W. Murphy, Mr. Trump’s appointee as the agency’s administrator, would start the official transition when it was clear that the race was over.“The G.S.A. administrator does not pick the winner in the presidential election,” Ms. Pennington said. “The G.S.A. administrator ascertains the apparent successful candidate once a winner is clear based on the process laid out in the Constitution.”Reporting was contributed by Jonathan Martin, Jim Tankersley, David E. Sanger and Katie Glueck. Joseph R. Biden Jr.’s advisers accelerated their transition planning on Friday as election results showed him with an advantage in battleground states that could hand him the presidency, with the first senior officials in a potential Biden White House possibly named as early as next week.In Wilmington and Washington, Mr. Biden’s advisers and allies are ramping up their conversations about who might fill critical posts, both in the West Wing and across the agencies, guided heavily by Mr. Biden’s plan to assemble what would be the most diverse cabinet in history.- Advertisement – Where they land is considered one of the early decisions that would help determine other appointments. Mr. Sullivan, a former adviser to Hillary Clinton, is lined up for one of a number of posts, while Mr. Blinken, who served as national security adviser to the vice president, is considered the leading candidate for national security adviser.Some of the most powerful cabinet positions in a possible Biden administration already have perceived front-runners.The top candidate to lead the Defense Department is Michèle Flournoy, a former under secretary of defense for policy who worked with Biden officials during the campaign. She would be the first woman ever to be appointed to the job. Susan Rice, a former national security adviser during the Obama administration whom Mr. Biden vetted for vice president, has been considered a leading choice for secretary of state, but the threat of Senate Republicans blocking her from becoming the nation’s chief diplomat in 2012 led to her withdrawal, and her nomination now would surely set off a fight.Mr. Blinken, a former deputy secretary of state, has been discussed among Biden allies as a possible choice, along with Senator Chris Coons of Delaware, a top Biden supporter who in October wrote an article in Foreign Affairs magazine on his worldviews.Representative Cedric Richmond of Louisiana, one of Mr. Biden’s campaign co-chairs and an adviser, is widely expected to take some role in the White House if the Democratic nominee wins. Another campaign co-chair, Mayor Eric Garcetti of Los Angeles, who also served on Mr. Biden’s search committee for vice president, could join a prospective administration, though it was not clear what post might lure him to Washington.Leaders of the Biden transition are aware that many civil servants throughout the federal bureaucracy have become demoralized and have felt marginalized during the Trump administration. In a small gesture, they are calling their potential first arrivals at agencies “agency review teams,” as opposed to what the Trump operation called “landing teams” in 2016. Updated Nov. 6, 2020, 10:06 p.m. ET – Advertisement – Transition officials are also looking at what types of economic actions could be taken almost immediately, including rolling back some of Mr. Trump’s executive orders, part of a tradition in which new presidents move quickly to change or reverse regulations across federal agencies. Already hanging over the discussions are the midterm elections, in 2022, which have traditionally been a struggle for whichever party holds the White House and which could be especially complicated for Democrats during an era of increasingly common progressive primary challenges.