The City University of New York has long spent much of its energy and resources just teaching new students what they need to begin taking college-level courses.

But that tide of remedial students has now swelled so large that the university’s six community colleges  like other two-year schools across the country  are having to rethink what and how they teach, even as they reel from steep cuts in state and local aid.

About three-quarters of the 17,500 freshmen at the community colleges this year have needed remedial instruction in reading, writing or math, and nearly a quarter of the freshmen have required such instruction in all three subjects. In the past five years, a subset of students deemed “triple low remedial”  with the most severe deficits in all three subjects  has doubled, to 1,000.

The reasons are familiar but were reinforced last month by startling statistics from state education officials: fewer than half of all New York State students who graduated from high school in 2009 were prepared for college or careers, as measured by state Regents tests in English and math. In New York City, the proportion was 23 percent.