NEW HAVEN, Conn.  — Yale University said Monday it is joining an expanding group of elite colleges under pressure from parents, lawmakers and alumni to make top schools more affordable to middle-class and upper-middle-class families.

The Ivy League school announced what it called the largest increase in financial aid spending in its history, boosting contributions from its endowment by more than $24 million to more than $80 million annually.

The move will reduce the average cost by more than half for families with financial need, Yale officials said.

About 43 percent of Yale's 5,300 undergraduates qualify for financial aid, said spokesman Tom Conroy. Yale's tuition is about $45,000 a year.

"Yale should be a college of choice for the very best and brightest students from across America and around the world, regardless of financial circumstances," Yale President Richard Levin said in a statement. "We want all of our students to make the most of Yale — academically and beyond — without worrying about excessive work hours or debt. Our new financial aid package makes this aspiration a reality."

The changes go into effect in the fall.

In making the announcement, Yale joins a group of elite schools — including rival Harvard — in boosting financial aid.

Harvard announced last month that it will provide $20 million more in financial aid. Harvard's tuition, room and board are $45,600 a year.

Duke earlier announced a plan to spend an extra $13 million on aid by capping loans and eliminating any required parental contribution from families earning less than $60,000.

The University of Pennsylvania, Pomona, Swarthmore and Haverford all announced they would eliminate loans, more than doubling the small number of schools promising all students a debt-free graduation.

Yale, which has the second biggest endowment in the nation, also announced that it would keep the increase in its tuition, room and board charges in 2008-2009 to the expected level of the consumer price inflation of 2.2 percent.