Things are not much better this semester. Ms. Macario, 18, who is majoring in psychology at Santa Monica College, left the crowded apartment in Los Angeles that she shared with her immigrant family from Guatemala and has been crashing with her sister and friends. But the Wi-Fi is unreliable, she is living too far away from her hospital internship, and she toils to tap out exams and homework on her phone.

“Between the internet, Covid and couch surfing, I haven’t been able to do a good semester,” Ms. Macario said.

Trapped between the financial hardships of the pandemic and the technological hurdles of online learning, the millions of low-income college students across America face mounting obstacles in their quests for higher education. Some have simply dropped out, as Ms. Macario did previously, while others are left scrambling to find housing and internet access amid campus closures and job losses.

“Every part of this pandemic is hitting low-income students hardest, and they were already in bad shape to begin with,” said Sara Goldrick-Rab, the founding director of the Hope Center for College, Community and Justice at Temple University, which studies the economic challenges facing college students.

Some colleges and universities have increased financial aid to students in need, but others, facing their own financial challenges, have said they cannot afford to offer more. A federal stimulus package passed in March that provided $7 billion for student expenses such as food, housing and health care has largely been depleted, and Republicans have balked at passing further relief proposed by Democrats. President Trump pulled out of and then tried to restart negotiations for additional aid last week.

The impact on struggling students can be seen most clearly at the nation’s roughly 1,400 community colleges, where nearly half of students start seeking degrees. Enrollment there declined by 8 percent this fall, compared with a 2.5 percent drop in undergraduate enrollment over all, according to the National Student Clearinghouse Research Center in Herndon, Va., which tracks college enrollment data.

The decline amounts to about half a million fewer community college students, said Martha Parham, a spokeswoman for the American Association of Community Colleges, an advocacy group in Washington. Unlike in previous economic recessions, when community colleges saw a surge in enrollment, the pandemic has had the opposite effect.

Most community college students work, Ms. Parham said, and many are parents. Home internet access and computers are sometimes unaffordable for them.

“If they have lost their job because of the pandemic, now they’re faced with, ‘How do I pay rent, how do I feed my kids?’” Ms. Parham said, adding that for those students “classes are not a top priority right now.”

For students who do drop out, there is little chance they will return. Just 13 percent of college dropouts re-enroll in courses, according to a report released last year. “Once you stop going,” Ms. Parham said, “it’s much more difficult to start back up again.”

Black and Latino students have been hit particularly hard. EAB, an educational research firm based in Washington, found that students of color had submitted a free application for federal student aid at far lower rates in 2020 than in previous years. The firm’s researchers also found that far more low-income students, particularly students of color, had committed to colleges but not shown up compared with last year.

One of those students is Jared Sawyer, 23, who was planning to begin his senior year at Morehouse College in Atlanta this fall but could not afford tuition. The son of a truck driver and an elementary schoolteacher, Mr. Sawyer largely relied in past years on financial aid, which often arrived just before the semester started. “Now it’s like 10 times worse,” he said.

Mr. Sawyer said his aid request to the college was denied in August with only a day’s notice. “They were like, ‘You have to come up with $10,000 by the end of tomorrow, or you’re no longer going to be enrolled,’” he said.

Morehouse did not respond to requests for comment. But the pandemic has strained the already-tight resources of many historically Black colleges and universities, making it harder for them to offer their students financial aid. Nearly three in five attendees at H.B.C.U.s are low-income, first-generation students, and over 70 percent of their students have limited financial resources.

Mr. Sawyer, who wants to become a pastor, is using his time off to work for civil rights organizations and to fund-raise so that he can re-enroll in the spring and obtain a doctorate in theology. “It’s definitely a delay, but sometimes stumbling blocks come,” he said.

Many students like Mr. Sawyer have been looking for alternative ways to pay for their education. As the coronavirus was closing campuses this past spring, Rise, a student-led organization that advocates college affordability, created an online network to help students find emergency financial aid, apply for public benefits and locate food pantries.

Rise has continued to serve more than 1,000 students a month who have struggled to pay rent, keep jobs and secure internet access, said Max Lubin, the organization’s chief executive. “We’re overwhelmed by the need,” he said.

Stable housing and healthy food were already major concerns before the pandemic. A 2019 survey found that 17 percent of college students had experienced homelessness in the past year, and about half reported issues such as difficulty paying rent or utilities. Nearly 40 percent lacked reliable access to nutritious food.

The coronavirus crisis worsened many of these challenges, according to a June report by the Hope Center, which found that nearly three out of five students surveyed had trouble affording basic needs during the pandemic.

Financial aid in the United States had already been stretched thin by the rising costs of tuition, room and board. At their maximum, need-based federal Pell grants cover 28 percent of the total cost of attending a public college today, compared with more than half of that cost in the 1980s. State aid, while recovering somewhat since the Great Recession, still falls short of need, and state budgets have been further drained by the health crisis.

The CARES Act, passed by Congress in March, provided about $14 billion for higher education, with about half earmarked for students. But there were limits on who could receive it, and college students were ineligible for the $1,200 stimulus check that went to taxpayers.

In a survey of some 300 college and university presidents conducted by the American Council on Education, a trade group, about 80 percent reported that they had provided more financial aid for the fall term. But few institutions have endowments large enough to cover significant increases, and many that do have traditionally been unwilling to cover living expenses.

“The whole system right now is built around the idea that the main cost is supposed to be the tuition, even though it’s not,” said Ms. Goldrick-Rab of the Hope Center.

Before the pandemic, Matt Bodo, 22, was homeless for two years while taking community college classes and working full-time as a waiter and a valet in Northern California. He was occasionally able to sleep on a friend’s sofa, but he mostly lived in his car, a rusted old Ford Mustang.

For internet access, he would spend as much time as possible on campus, where he could also shower.

Last year, Mr. Bodo transferred to the University of California, Los Angeles, where he is majoring in linguistics and psychology, and settled into a shared dorm room. But he could not afford the cost for housing after the pandemic hit and the school required students to pay more for single rooms.

His younger sister, a community college student in the Bay Area, lost her housing in early April, and he returned to help her. Few of his quarantining friends were willing to take them in, so soon they were both sleeping in their cars.

This term has been somewhat better; nonprofit groups have helped him afford a U.C.L.A. dorm. But even with financial assistance and three jobs, Mr. Bodo is struggling to pay for classes and to support his sister, who is still couch surfing and needs money for community college.

If he cannot make ends meet, Mr. Bodo said, he will become homeless again in order to cover her rent.

“She’s my little sister, and I hate to see her struggle,” he said. “In my heart, I put her before me, even if that means I’m living in my car.”