Swarthmore College is in rare company nationally as a school that collects nearly as much or more revenue from investments as it does from students.

Its $1.5 billion endowment - about $1 million per student - allows the highly ranked college to spend more on each student, but it does not fully shield Swarthmore from the economic forces threatening higher education.

"When we think about the future, we're worried about . . . economic growth in this country," said Suzanne Welsh, vice president for finance and treasurer at Swarthmore.

The economy has grown, but "it's not showing up in growth in family incomes to any large extent. That affects how much families can pay in tuition," Welsh said.

That worry about tuition dollars at Swarthmore, where endowment income typically accounts for 40 percent of the operating budget, could turn into a full-blown financial crisis for schools that depend heavily on tuition to pay bills unless they change the way they operate.

The dismal state of family incomes - lower in the Northeast than they had been since 1997 in inflation-adjusted terms - is not the only factor making college executives sweat.

A multiyear decline in the number of annual high school graduates, fatigue from ever-rising tuition bills, and increased public scrutiny caused by climbing student-loan default rates have knocked higher education off balance.

"A lot of the revenue sources just don't look promising for colleges and universities," said John Cheslock, director of Pennsylvania State University's Center for the Study of Higher Education.

Four-year private colleges and universities in the Philadelphia area, where higher education is counted as an economic anchor, have already seen a significant drop in revenue trends, as they've had to sharply increase discounts and financial aid to attract and keep students on campus.

In each of two years ended June 30, 2012, net tuition collected from students and their families - after institutional financial aid and adjusted for inflation - at 20 area private schools rose less than 1 percent on average, financial statements and bond disclosures show.

In the three years before that, the inflation-adjusted median gains - meaning half did better and half did worse - ranged from 2.6 percent to 6.7 percent in 2009, when colleges were helped by a recession-induced enrollment spike, an analysis by The Inquirer found.

Some schools, including Chestnut Hill College and Rosemont College, are not required by their borrowing arrangements to disclose their consolidated financial statements. Both declined an Inquirer request for the documents.

The analysis also did not include highly specialized institutions, such as the University of the Arts and strictly religious schools.

The recent decline is even more dramatic compared with the period from 1990 through 2010. Area private schools averaged 4.5 percent annual growth in net tuition revenue during that period, the most recent federal data show.

Moody's Investors Service this year expanded its negative outlook on the higher-education sector to include market-leading diversified colleges and universities. The outlook on the rest of the sector had been negative since 2009.

"The new sector-wide negative outlook reflects mounting pressure on all key revenue sources, requiring bolder actions by university leaders to reduce costs and increase operating efficiency," the ratings agency said.

Even for schools with a strong credit rating, such as Bryn Mawr College, a top liberal arts school with a $645 million endowment, net tuition has barely budged over the last five years on an inflation-adjusted basis.

Over the same period, undergraduate financial aid climbed 52 percent, to $24.4 million in fiscal 2012 from $16 million in fiscal 2007, and the school's operating margin shrank to nearly zero.

"As the economy recovers, our margins have begun to improve and we expect them to improve more this year," said Laurie Koehler, Bryn Mawr's dean of admissions and interim dean of enrollment.

Bryn Mawr - whose president is leaving after five years, the shortest tenure in the school's history - said in a financial summary for fiscal 2012: "Net undergraduate tuition is the most serious concern to the college's financial stability."

Most schools without big endowments are looking beyond traditional undergraduates for revenue.

Gwynedd-Mercy College, which gets from 85 percent to 95 percent of its revenue from tuition and is among the few smaller schools in the region to keep expenses in check relative to tuition revenue trends, started an adult-accelerated program in the late 1990s.

"There's been significant growth over the last seven years," said Kevin O'Flaherty, Gwynedd-Mercy's chief financial officer. "It's kind of plateaued now."

The next frontier is "getting more fully into online programs. That's what the market's telling you," O'Flaherty said.

Philadelphia University, where the rate of growth in tuition revenue has fallen for four straight years, is counting on graduate programs in sustainable design, geodesign, and other areas, plus continuing and professional studies, president Steve Spinelli said.

The school in the East Falls section offers those courses of study on campus, online, and in a hybrid of both. "If you do all of those efficiently and effectively, then I think the market is growing," Spinelli said.

Over the last five years, graduate school credit hours at Philadelphia University are up 47 percent and graduate revenue is up 74 percent, to $12.5 million from $7.2 million.

As to undergraduate programs, "we're not looking for any substantial growth there," Spinelli said.

Ursinus College, by contrast, is sticking to its focus on undergraduates, said Richard DiFeliciantonio, vice president for enrollment at the Collegeville liberal arts school. Ursinus gave almost as much student aid as it collected in tuition in 2012.

Ursinus, which has a small endowment of $105 million, is engaged in strategic planning to fortify its liberal arts tradition despite the sector's turmoil.

"The market is extremely variable and in flux, and extremely difficult to predict," said DiFeliciantonio. "There's no simple place for us to go."

At DiFeliciantonio's alma mater, Swarthmore, the path to the future seems much smoother, but it is not immune to risk.

"People think that if a school has a large endowment, they don't have to worry about money," said Welsh, "but the fact is that each year we're using as much as we think is prudent and we've built a program around that. We're using it all each year."