As President Trump and his team dialed up the pressure on Harvard University last month, threatening to bar its international students, the school issued what was at once a warning and a plea.

“Without its international students, Harvard is not Harvard,” school officials wrote in a lawsuit asking a judge to stop the federal government’s actions.

It left unsaid what Harvard, if it were no longer Harvard, would become.

It’s a scenario that some inside Harvard are beginning to imagine and plan for as the Trump administration lobs attacks from all angles, seeking to cut the university off from both students and billions of dollars in federal funding.

Top leaders at Harvard, one of the nation’s oldest universities, including its provost, John F. Manning, a conservative legal scholar who once clerked for the former Supreme Court justice Antonin Scalia, are meeting more frequently to strategize.

The school’s board of trustees, the Harvard Corporation, has discussed whether hundreds, if not thousands, of people will need to be laid off.

And on 8:30 a.m. Zoom calls once or twice a week, administrative officials meet with senior leaders of Harvard’s undergraduate and graduate schools to share updates about the latest Trump developments, which keep coming rapid-fire.

Individual schools at Harvard are also making their own contingency plans. The Harvard Business School is considering moving some classes online if foreign students are barred. Facing a loss of federal funding, the T.H. Chan School of Public Health is pursuing corporate sponsors, who officials hope would sponsor Ph.D. students and post-doctorate fellows for $100,000 a year.

Several officials inside Harvard described the ways the university is planning, even as a rapidly changing situation has made it hard to see very far into the future.

Most recently, Mr. Trump issued a presidential proclamation that would bar Harvard’s international students from entering the country. Those students make up 15 percent of Harvard’s undergraduate population, and as much as a third to half of some graduate schools. Without them, Harvard would not only lose students and the tuition that comes with them, but also its status as a gathering place for the world’s brightest minds.

“We would lose influence all over the world,” said Lawrence H. Summers, who was president of Harvard from 2001 to 2006. “Instead of being the world’s pre-eminent university, after a few years, Harvard would be just another school.”

From No. 1 to just another school

By some measures, Harvard is No. 1 in the world for research, followed by 10 universities in China. After the Trump administration said it would end the school’s federal funding for research, Harvard began making plans to scale back significantly, potentially ceding ground to international competitors.

The Trump administration and Republicans in Congress are also weighing changes to how much Harvard would have to pay in taxes, including a major increase in the tax on Harvard’s endowment. Mr. Trump has also floated the idea of taking away Harvard’s tax-exempt status entirely, although that proposal faces major hurdles. (The president cannot make the decision to revoke the tax exemption himself.)

Even if only some of the scenarios came to pass, experts say, Harvard could be left in a weakened position with few modern comparisons.

It would still be a big, Ivy League institution with a student body larger than, say, Dartmouth, which has 7,000 students, compared with Harvard’s 24,500 today.

But without federal dollars or international talent, experts say, Harvard could fall out of the top tier for research, where it currently sits with competitors like Stanford University and the Massachusetts Institute of Technology. By sheer dollars spent, its research budget could shrink to something similar to that of the University of Illinois Urbana-Champaign, which spent just over $800 million on research in 2023, roughly half of what Harvard spends now.

And no major university has faced losing its tax-exempt status, a move that would transform Harvard into a taxpaying corporation.

Mr. Trump’s moves are hard to predict. Harvard and others are challenging the administration’s directives, and it’s unlikely that administration officials will be able to follow through on every threat.

Legal experts have said the university’s case to restore its funding cuts is strong. But the Trump administration has also said it would decline to fund Harvard in the future, something that could be harder for the school to challenge.

Harvard could choose to negotiate. But inside the university, officials appear reluctant to do that, given the backlash they could face for capitulating to Mr. Trump. This spring, the university took out $750 million in debt, giving it some cash flow as court decisions play out.

The atmosphere is particularly tense inside the Harvard T.H. Chan School of Public Health, which relies on federal funding for 46 percent of its budget and has a student body that is about 40 percent international. Senior officials there are planning for the worst, and have called the potential changes an “existential crisis” for the school’s future.

The school is taking out a loan from the university, aggressively wooing new philanthropic dollars and cutting research by about 50 percent for next year.

The school’s dean, Dr. Andrea Baccarelli, laid out the dire situation in an email to the school’s faculty and staff this month. “We must adapt to a new world,” he said.

Harvard would lose revenue from 3 key sources

Mr. Trump and his team have targeted Harvard for what they say are violations including allowing antisemitism, discriminating on the basis of race in admissions and fostering a culture intolerant to conservative viewpoints. The administration is seeking oversight measures at the university.

Harvard has denied many of the government’s accusations and resisted its demands.

In response, the Trump administration cut all federal research dollars to Harvard, which equaled $686 million last year, or 11 percent of its total revenue. The Trump administration is also going after international students, and thus a key source of tuition revenue, because those students often pay full price.

But Harvard’s biggest source of funding is donations and payouts from its endowment, which together make up 45 percent of its revenue.

Republicans are targeting those funds as well. Harvard would pay significantly higher taxes under a Republican proposal moving through Congress to increase taxes on endowment earnings. Harvard’s taxes would rise to 21 percent, from 1.4 percent.

Republicans have said the goal is to hold accountable “woke, elite universities that operate more like major corporations.”

Liz Clark, vice president for policy and research at the National Association of College and University Business Officers, said the change would most likely mean less money for financial aid.

Harvard is the richest university in the world, with an endowment of $53.2 billion.

But legally, it cannot use most of the money to cover shortfalls, said Larry Ladd, a former budget officer at Harvard.

“Trump has pulled off something I thought I’d never see, which is he made Harvard look sympathetic,” said Richard D. Kahlenberg, a Harvard critic who supports the idea of giving admissions preferences to students with lower family incomes.

Harvard could become even more of a haven for the wealthy

Republicans have pointed to Harvard’s elite status in their criticism of the university. But in a worst-case scenario for the school, experts say, it could become even more expensive.

Harvard has historically had three times as many students from the top 1 percent of family income as from the bottom 20 percent.

But in recent years, it has tripled the share of students who are the first in their family to go to college — a group that is more likely to be lower-income or middle-class — to 20 percent, from 7 percent. Harvard also recently announced it was expanding financial aid, offering free tuition to undergraduates from families making $200,000 or less.

Harvard officials have not backed away from that promise. But they have acknowledged in court paperwork that, in certain extreme scenarios, students could lose access to financial aid.

The endowment tax alone would put pressure on the university. And without international students, it is possible that some of the university’s expenses would have to be absorbed by remaining students.

“It would become a more sheltered and elite place,” said Ted Mitchell, president of the American Council on Education.

Mr. Kahlenberg said his “big fear” was that Harvard might scale back on social mobility efforts and seek to admit more students whose families could pay full freight, nearly $87,000 a year for undergraduates, including room and board.

A Harvard spokesman declined to comment.

What is Harvard without its research might?

Perhaps the biggest change already underway at Harvard is the loss of federal research dollars, more than $3 billion in all.

What is Harvard without it?

Insiders do not believe Harvard will become just a liberal arts college. But it will almost certainly do less research.

Of nearly $1.5 billion spent on research at Harvard last year, nearly half was from the federal government.

Private philanthropy and corporate investments, plus research paid for by the university itself, would continue. But Harvard most likely could not make up for the scope of federal losses with its own dollars or even a major philanthropic investment.

At Harvard Medical School, federal dollars have been crucial to research discoveries on Alzheimer’s disease, non-opioid treatments for pain and cancer immunotherapy, the dean, Dr. George Q. Daley, said. About 60 percent of research at the school is funded by the federal government.

The school is now advising scientists to shrink the number of projects they’re working on.

Cutbacks at Harvard may not translate to a boon for other U.S. universities, however, because the Trump administration is also pursuing dramatic cuts to the National Institutes of Health and the National Science Foundation, which would mean less money for everyone. “We might as well just grant the future of biotechnology and pharmaceuticals, quantum computing, A.I. and technology to China,” Dr. Daley said.

Some researchers are turning to the private sector to try to keep their labs afloat, but even that may be in jeopardy if the university loses its tax-exempt status.

“The likelihood that people are going to want to contribute charitable funds is significantly diminished,” said David R. Walt, a professor at Harvard Medical School who lost federal funding for research developing a technology to detect the presence and progression of Lou Gehrig’s disease, or A.L.S. He is pursuing private philanthropy to try to replace some of the lost funding.

Still, some observers have optimism for a school that has been around for close to 400 years.

“If all of this comes to pass, the incredibly smart people at Harvard will decide to reinvent Harvard,” said Mr. Mitchell of the American Council on Education.

What that may look like, though, is anyone’s guess. “It’s not like just deflating a balloon and becoming smaller,” he said. “It would be a restart.”