Financial experts everywhere agree that the economy appears headed toward a recession. The question is how long it will last and how deep it will be. The last recession, in 2001, lasted less than a year. Most sectors, including higher education, shrugged it off. During lengthier downturns, colleges have often benefited from increased enrollments. What better place than an ivy-lined campus to retreat, or to stay put, when the job market goes south? But for some institutions, those enrollment increases are not a panacea. And if this recession lasts as long as some economists fear, colleges of all kinds could experience a variety of problems, finance experts and campus leaders said in e-mail and telephone interviews. Wealthy private colleges can often sidestep problems by tapping into their multi-billion-dollar reserves and hedging their investments. Big public institutions usually have enough diverse revenue sources, including federal research grants, to stay out of trouble. But many experts fear that state support and federal research dollars will decline for the foreseeable future. As a result, even big public institutions could face problems. And the picture is even bleaker for private colleges without big endowments or research support to pad them. When state finances tighten up, support for higher education often dwindles. In the past, many colleges have helped overcome those shortfalls by raising tuition. But increasing frustration over rising tuition costs, coupled with families' inability to pay more during downturns in the housing and stock markets, may make that increasingly difficult. Low-income students at community colleges would be particularly hard-hit. And increasing student aid will be more difficult for colleges if investment income erodes. Student populations are expected to become more diverse and more dependent on aid in coming years, while traditional students will continue to demand more services, changes that alone could lead to big cost increases for institutions. But in combination with a weak economy, declining federal grants, and increased competition for talent, they could prove even more ominous.