tax increases, they are working to influence a final product that many of them may ultimately refuse to support.

“I think all of us would agree that we need a robust infrastructure package that focuses on roads, bridges, airports, seaports, water systems and broadband, but this proposal goes way beyond that,” Senator Susan Collins, Republican of Maine and a member of a bipartisan group searching for compromise, said in an interview. “It seems to me that our first goal should be to try to shape the package and reduce its cost.”

Mr. Biden and Democrats have repeatedly challenged Republicans to engage in bipartisan negotiations. By incorporating Republicans’ proposals, including individual projects for their districts and states, Democrats hope to increase the political risks of voting against the bill. Some Republicans are already facing criticism for celebrating funding in the nearly $1.9 trillion pandemic relief package they unanimously opposed.

Yet the infrastructure measure has a far more bumpy path to enactment than the stimulus package, which Democrats muscled through last month without any Republican votes. With narrow majorities in both chambers and conflicting ambitions for what could be one of the few major legislative vehicles this year, Democratic leaders are facing a steep challenge in steering the package through Congress.

suggested bringing back Build America Bonds created after the Great Recession to help states and cities borrow money for infrastructure projects. Senate Democrats have unveiled their own plans to pay for parts of the package by raising taxes on multinational corporations that stash profits overseas.

“I think everyone realizes that we have to come together because failure is not an option,” Senator Chuck Schumer of New York, the majority leader, said in an interview. The administration, he said, is “going to talk to many members — it is a big, broad bill — and try to incorporate some good ideas that other members have, too.”

Mr. Schumer noted that the Biden administration had already included two of his priorities — funding to transition to clean cars and legislation meant to strengthen American technology investments and research — in the package, and will most likely accommodate other changes.

Mr. Buttigieg would not provide specifics on how officials would choose which transportation projects would get funding. But he said there would most likely be a mix of ways to fund proposals, including through existing grant programs and the creation of new funding streams.

In an email sent to congressional lawmakers last week, officials from the Transportation Department provided preliminary details on how $621 billion of Mr. Biden’s proposal could be spent on transportation and infrastructure projects. The largest allocations included $174 billion for electric vehicles, with another $115 billion to repair and build roads and bridges.

Officials proposed $85 billion for public transit, $25 billion for airports and $17 billion for ports and waterways. The email, obtained by The New York Times and first reported by Roll Call, stressed that the numbers outlined were preliminary and could be revised during negotiations.

opportunities to reduce racial inequity caused by highway construction.

which face a nearly 40-year backlog of repairs, will have no shortage of competition for funding. Projects that already have local tax funds approved, such as a $54 billion initiative to expand light-rail systems across the Seattle region, could also be competitive for federal funding, experts said. Amtrak officials have signaled that they could expedite the creation of a national rail service that reaches an additional 160 communities in the United States.

Beth Osborne, the director of Transportation for America, an advocacy group, said the process of sorting through the competing priorities to produce the package will be a grueling one.

“God bless these staffers and members who have to figure this out,” said Ms. Osborne, a former Senate aide who helped work on the 2009 stimulus law. “On one hand, it’s going to be tough. On the other hand, this is why people come to D.C. to work.”

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