The long enrollment boom that swelled American colleges — and helped drive up their prices — is over, with grim implications for many schools.

College enrollment fell 2 percent in 2012-13, the first significant decline since the 1990s, but nearly all of that drop hit for-profit and community colleges; now, signs point to 2013-14 being the year when traditional four-year, nonprofit colleges begin a contraction that will last for several years. The college-age population is dropping after more than a decade of sharp growth, and many adults who opted out of a forbidding job market and went back to school during the recession have been drawn back to work by the economic recovery.

Hardest hit are likely to be colleges that do not rank among the wealthiest or most prestigious, and are heavily dependent on tuition revenue, raising questions about their financial health — even their survival.

“There are many institutions that are on the margin, economically, and are very concerned about keeping their doors open if they can’t hit their enrollment numbers,” said David A. Hawkins, the director of public policy and research at the National Association for College Admission Counseling, which has more than 1,000 member colleges.