WASHINGTON — President Biden and congressional Democrats vowed on Wednesday to push through a $3.5 trillion budget blueprint that would shepherd a transformative expansion of social and environmental programs into law, beginning an arduous drive to enact their vision for extending the reach of public education and health care, taxing the rich and trying to stem the warming of the planet.
The legislation is far from reality yet, but the details top Democrats have coalesced around are far-reaching. Prekindergarten would be universal for all 3- and 4-year-olds, two years of community college would be free, utilities would be required to produce a set amount of clean energy and prescription drug prices would be lowered. Medicare benefits would be expanded, and green cards would be extended to more undocumented immigrants.
At a closed-door luncheon in the Capitol, Mr. Biden rallied Democrats and the independents aligned with them to embrace the plan, which would require each of their votes to move forward over united Republican opposition. Yet crucial moderates had yet to tip their hands about whether they would welcome such an expansive proposal.
Mr. Biden’s message to senators, said Senator Richard Blumenthal of Connecticut, was that Democrats “need to be unified, strong, big and courageous.”
“We’re going to get this done,” Mr. Biden told reporters at the Capitol.
The Senate could begin advancing the plan in weeks, though a final vote could be months away and will face multiple hurdles. For now, Democrats and their independent allies insist they are together, even as moderates declined to commit to the package without further details.
Speaker Nancy Pelosi, who must ultimately get the package through a narrowly divided House, told Democrats in a letter on Wednesday: “This budget agreement is a victory for the American people, making historic, once-in-a-generation progress for families across the nation.”
Senate Democratic leaders have said they aim to pass both the budget blueprint and a narrower, bipartisan infrastructure plan that is still being written before the chamber leaves for the August recess, an extraordinarily complex and politically charged endeavor in a 50-50 Senate.
“This is a moment in history when the United States needs to reassert itself in how we deal with families, how we deal with our children, with the existential crisis of climate change and how we deal with China,” Senator Mark Warner, Democrat of Virginia and one of the key negotiators, told reporters on Wednesday.
Combined with the infrastructure plan, the social spending is intended to deliver on Mr. Biden’s $4 trillion economic proposal. Democrats on the Senate Budget Committee must produce a budget resolution in the coming days that includes so-called reconciliation instructions to other Senate committees, which in turn will draft legislation detailing how the $3.5 trillion would be spent — and how taxes would be raised to pay for it.
That would pave the way for Democrats to produce a reconciliation bill this fall that would be shielded from a filibuster, allowing them to circumvent Republican opposition but requiring all 50 of their members — and a majority in the narrowly divided House — to pass it.
The reconciliation package would be stuffed with liberal priorities, including an expansion of Medicare to include dental, vision and hearing benefits, clean energy provisions, paid leave and home care — all paid for with tax increases on wealthy individuals and corporations.
In the private lunch, Senator Chuck Schumer of New York, the majority leader, outlined the contours of the proposal and the directives it would lay out.
Democrats included the creation of a “civilian climate corps” to create jobs in addressing climate change and conservation, providing for child care, home care and housing investments.
They would also extend some temporary provisions from the $1.9 trillion pandemic relief package, most notably monthly payments for all but the wealthiest families with children and expanded subsidies for Americans buying health insurance through the Affordable Care Act.
Huge investments would go to renewable energy and a transformed electrical system to move the U.S. economy away from oil, natural gas and coal to wind, solar and other renewable sources. The budget blueprint is to include a clean energy standard, which would mandate the production of electricity driven by renewable energy sources, and would bolster tax incentives for the purchase of electric cars and trucks.
To fully finance the bill, it is expected to include higher taxes on overseas corporate activities to alleviate incentives for sending profits overseas, higher capital gains rates for wealthy individuals and higher taxes on large inheritances, and stronger tax law enforcement.
Most of the specific details will be hammered out after the budget resolution is written and passed through both chambers.
Specific provisions will have to pass muster with the strict budgetary rules that govern the reconciliation process, which require that provisions affect spending and taxation, not strict policymaking. That could doom the clean energy standard, the provision most desired by climate activists and many scientists.
Moderate Democrats, who had balked at a progressive push to spend as much as $6 trillion on Mr. Biden’s entire economic agenda, largely declined to weigh in on the blueprint, saying they needed to see more than an overall spending number.
“We’ve got to get more meat on the bones for me,” Senator Jon Tester, Democrat of Montana, told reporters. “I’ve got to get more information on what’s in it.”
The size of the blueprint could be shaped by the success or failure of the bipartisan infrastructure plan, which would devote nearly $600 billion in new spending to roads, bridges, tunnels and transit. The group of lawmakers negotiating that package has yet to release legislative text as they haggle over the details of how to structure and pay for the plan.
But some Republican negotiators conceded that the progress on the broader social spending bill intensified pressure on them to come to terms on the infrastructure plan. If Republicans cannot deliver enough votes to move the package past a filibuster, Democrats would just move it into the reconciliation plan and take away any chance for Republicans to shape it, said Senator Rob Portman of Ohio, one of the negotiators of the bipartisan bill.
“If we don’t pass infrastructure, they’re going to put even more infrastructure in than we have and worse policies,” said Mr. Portman, who fielded skepticism from his colleagues in a private Republican lunch on Tuesday. “It’s not just about spending. It’s about policy. That’s just the reality.”
Some Republicans had hoped that a bipartisan accord on physical infrastructure projects would drive moderate Democrats away from a multi-trillion-dollar reconciliation package. But it might be doing the opposite — bringing Republicans on board the one piece of legislation they can influence.
“I want to be able to tell people in South Carolina: I’m for this, I’m not for that,” said Senator Lindsey Graham of South Carolina, the top Republican on the Senate Budget Committee and a peripheral presence in the bipartisan talks.
He added that the lengthy floor debate over the blueprint would allow Republicans to “ferociously attack it, to have amendments that draw the distinctions between the parties, to scream to high heaven that this is not infrastructure.”
Senator Joe Manchin III of West Virginia, the centrist Democrat whose support might be determinative, released a noncommittal statement Wednesday, saying only: “I know my Democratic colleagues on the Budget Committee have worked hard, and I look forward to reviewing this agreement. I’m also very interested in how this proposal is paid for and how it enables us to remain globally competitive.”
Senator Kyrsten Sinema, Democrat of Arizona and another key moderate, also hung back on Wednesday, when her office said she would decide whether to support the proposal based on what was included.
Still, the $3.5 trillion package had plenty in it to appeal to senior Democrats who were eager to use it to advance their longtime priorities. For Senator Patty Murray of Washington, the chairwoman of the Health, Education, Labor and Pensions Committee, it was an extension of a more generous child tax credit, as well as subsidies for child care, prekindergarten, and paid family leave.
For Senator Bernie Sanders, independent of Vermont and the Budget Committee chairman, it was the Medicare and climate provisions.
“Finally, we are going to have America in the position of leading the world in combating climate change,” he said, calling the package “by far the most significant effort this country has ever seen” to combat climate change.
Mr. Tester said the need for school construction was so high that trillions could go to that alone.
The budget resolution is expected to include language prohibiting tax increases on small businesses, farms and people making less than $400,000, fulfilling a key promise Mr. Biden has maintained throughout the negotiations.
Jim Tankersley, Lisa Friedman and Nicholas Fandos contributed reporting.