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

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 cut the average cost more than in half for families with financial need, Yale officials said.

About 43% of Yale’s 5,300 undergraduates qualify for financial aid, a spokesman, Tom Conroy, said. Tuition, room, and board at Yale total 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,” The president of Yale, 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 total $45,600 a year.

Duke earlier announced a plan to spend an extra $13 million on aid by limiting 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, whose endowment of $22.5 billion is the second largest in the nation after Harvard’s, also announced that it would keep the increase in its tuition, room, and board charges in 2008-2009 to the expected level of consumer price inflation of 2.2%.

Yale said it is increasing the number of families who qualify for aid, eliminating the need for students to take loans, enhancing its grants to families with more than one child attending college, exempting the first $200,000 of family assets from the assessment of need and increasing expense allowances for foreign students.

Yale officials announced last week that the school will spend more money from its endowment in the 2008–2009 academic year on financial aid and scientific research. The university intends to increase the annual endowment payout for such programs by 37% to $1.15 billion, Mr. Levin said.