Dartmouth College will lay off 60 employees after its endowment fell 18 percent, part of the school’s plan to cut its $700 million operating budget by $72 million between now and 2011. Seventy more employees have accepted buyouts and 28 others will have reduced hours, Dartmouth officials said in a statement Monday. Most salaries will be frozen, and although no faculty positions are being eliminated, a third of current searches will be postponed. Tuition will rise 4.8 percent to $38,445, although the financial aid budget will also increase 13 percent.