WASHINGTON — On the campaign trail, Joseph R. Biden Jr. heavily promoted his plan to offer tuition-free community college. He pitched the proposal as crucial to his economic agenda — a way to rebuild the middle class, which he called the “backbone” of America.

Nine months into his presidency, Mr. Biden has conceded that the plan is dead for now, a concession to moderate Democrats whose votes are crucial to passing a pared-back version of a sweeping $3.5 trillion social safety net and climate bill.

At a CNN town hall on Thursday, Mr. Biden said the provision had to be dropped after Senator Joe Manchin III of West Virginia “and one other person” indicated that they would not support free community college. Instead, Mr. Biden said Democrats would focus on increasing the maximum federal Pell grant award and other forms of tuition assistance.

“It’s not going to get us there,” Mr. Biden said. “It’s not going to get us the whole thing, but it is a start.”

The bill would have committed $45.5 billion to waive two years of tuition at community colleges for a period of five years. States would have to opt in, and the federal government would cover the cost of the program for the first year. The federal contribution would decrease by 5 percent each year after that, with states covering the rest.

Paired with a separate plan to offer free prekindergarten for every 3- and 4-year-old in the country, the proposal was meant to benefit minority and low-income students in particular, who face higher economic barriers to obtaining a degree.

Democrats are still exploring expanding tuition assistance for low- and middle-income students. But how big a program they will support, and how far that approach will go toward increasing access to higher-paying jobs — and economic competitiveness overall — remains to be seen.

Arne Duncan, who served as education secretary in the Obama administration, said it was “heartbreaking” that tuition-free community college would most likely be left out of the bill because of how far it would have gone toward addressing inequality.

“This is the one play that would go a historic distance in leveling that playing field,” Mr. Duncan said. “I can’t believe this is what’s on the chopping block.”

Research has shown that waiving tuition at community colleges could lift not just enrollment among students who may not otherwise have attended college, but their wages for years to come. Eliminating tuition makes the decision to enroll much easier, economists and researchers said. The plan was also supposed to financially shore up the colleges themselves, which have suffered disproportionately during the pandemic.

Critics of the community college plan had pointed to high dropout rates and poor outcomes at some of the schools; fewer than 40 percent of community college students earn a degree within six years.

Free community college was not as prominent a priority as other proposals, and it faced opposition from key Democrats and interest groups, according to people familiar with the matter.

Students would have been eligible for free tuition and fees for a maximum of six semesters under the plan. Representative Pramila Jayapal of Washington, the chairwoman of the Congressional Progressive Caucus, said her members had hoped it would survive, not least because Jill Biden, the first lady, is a longtime community college professor.

“I was hoping that the first lady would carry that priority across the line,” Ms. Jayapal said.

In addition to expanding tuition assistance through Pell grants — which can go toward tuition, fees, books, room and board — and other means, the package will probably include some assistance for historically Black colleges and universities, according to two people who attended a meeting about the budget bill with Mr. Biden on Tuesday.

But those people, speaking on condition of anonymity to disclose details of a private conversation with the president, cautioned that it was unclear how much money would ultimately be put toward those programs.

The $3.5 trillion package already proposes increasing the maximum Pell grant award, now $6,495 per student a year, by $500.

Douglas N. Harris, who helped the Biden campaign research free-college programs around the country, said that while the increase in Pell grants would help students, it would not be enough to have a significant impact.

“$500 doesn’t go very far,” said Dr. Harris, chairman of the economics department at Tulane University. “It’s not going to substantially change the financial outlook of these students.”

Democrats could push for larger increases to the maximum Pell grant award or provide direct assistance to institutions, Dr. Harris said. But he said that passing a free community college program would probably require a larger political movement or more Democrats elected to Congress.

Veronica Bumpus, 27, a student at the BridgeValley Community and Technical College in South Charleston, W.Va, said she was disappointed after hearing that the proposal was dropped, and particularly upset with Mr. Manchin, her senator.

“I don’t understand where Joe Manchin is,” she said. “I don’t agree with him. He should feel how I feel.”

Ms. Bumphus, a single mother, said free college would allow her to cut back the hours she works at her part-time job, and to focus more on her schoolwork and her two-year-old son. She said it would also help her catch up on her electric, water and internet bills. Ms. Bumphus pays about $2,700 in tuition each semester, she said, after receiving about $1,000 from the West Virginia Invests grant program.

Pamelina Williams, 22, a student at the Milwaukee Area Technical College in Wisconsin, said she would like to transfer to a four-year college, but is not sure she can afford to. Having her tuition waived for now would make her “more inclined” to continue her education, she said.

“It would make it a lot easier for me to do that,” said Ms. Williams, a fellow with Rise, an organization that advocates for free community college.

A recent estimate from the National Student Clearinghouse Research Center found that community colleges were the hardest hit among all higher-education institutions, with enrollment dropping by 9.5 percent this spring. More than 65 percent of the total undergraduate enrollment losses in the spring occurred at community colleges, according to the report.

Celeste K. Carruthers, an associate professor of economics at the University of Tennessee, said that research on community colleges had shown that waiving tuition would most likely increase enrollment, as well as wages for people who completed their degrees.

Dr. Carruthers and her colleagues tracked the performances of students who were eligible for Knox Achieves, a program that provided free community college to any high school graduate in Knox County, Tenn., and found that eligibility for the program led to higher completion rates at two-year community colleges. It also led to significantly higher wages for as long as seven years after high school, according to the study.

Riley Acton, an assistant professor of economics at Miami University in Ohio who has studied community colleges, said waiving tuition across the board would make it easier for students to decide to attend community college. Many face barriers in applying for financial aid, given the complexities of the process.

“It’s not always made immediately clear to students that yes, that’s the advertised tuition rate, but if you fill out these forms and apply for these programs, that rate could be reduced,” Dr. Acton said.

Still, some worry that offering tuition-free community college could discourage people from getting four-year bachelor’s degrees.

“It could have done some damage in terms of pushing people into community colleges instead of four-year universities when that wouldn’t necessarily be the best option for everybody,” said Michael J. Petrilli, the president of the Thomas B. Fordham Institute, a conservative research organization.

Mr. Petrilli said he believed Mr. Biden’s plan was unnecessary, given that states can decide on their own whether to waive tuition and some already have. More than 15 states offer some form of free community college, mostly targeted to lower-income students.

The precursor to Mr. Biden’s plan was rolled out in 2015, when then-Vice President Biden and Jill Biden joined President Barack Obama at Pellissippi State Community College in Knoxville, Tenn.

L. Anthony Wise Jr., the president of Pellissippi State, which has 8,600 students, said that the proposal Mr. Obama announced that day was similar to Mr. Biden’s.

“For low-income, first-generation students, the textbook burden is pretty significant,” Dr. Wise said. “For adult learners, there are housing and child care expenses that can be a burden.”

Tennessee Promise, a state plan, provides funding for remaining tuition and fees that are not covered by Pell grants or other scholarships. Another program called Tennessee Reconnect assists adult learners who return to school.

While it was not entirely clear exactly how Mr. Biden’s plan would have worked, Dr. Wise had hoped to use the federal funds to help students with housing or food costs.

In Oregon, which provides annual tuition assistance of up to about $4,000 for low-income college students, Mark Mitsui, president of Portland Community College, said the extra funding would have benefited students. Even if the proposal is not adopted this year, he said it was important to have placed it on the table.

“There are going to be setbacks,” said Mr. Mitsui, whose system enrolls 60,000 students. “I think this is really an important first step and the main thing is to continue to push.”

Stephanie Saul and Emily Cochrane contributed reporting.