Despite the continuing economic slump, enrollment at private, nonprofit colleges is expected to increase slightly this fall compared with last year, according to a report to be released this week by the National Association of Independent Colleges and Universities. Undergraduate enrollment is anticipated to grow by 0.2 percent, with combined enrollments of undergraduates and graduate students increasing by 0.1 percent, said the report. The findings come from a survey of 284 colleges, most of them with enrollments below 5,000. The unpredictable economy is making this admissions season a guessing game, the report said. For one thing, more students than in previous years are angling for larger financial-aid packages. More than 80 percent of the colleges in the survey reported increases in student-aid applications.