Duke University, Davidson College, Wake Forest University and 25 other leading schools have agreed on more generous guidelines for determining eligibility for financial aid, the colleges will announce today.

The new guidelines, an effort to stave off a growing trend toward giving aid to the most desirable students, rather than just the neediest, are likely to result in higher scholarships, ranging from hundreds of dollars to more than $1,500 for many students, university officials said.

All the institutions agreed they will not reduce their total aid, although some individual students may receive less.

The 28 colleges and universities represent a significant portion of the selective private universities in the United States that admit students without regard to their ability to pay and provide them with financial aid to attend, a practice known as need-blind admissions.

Many of these colleges and universities charge more than $30,000 a year for tuition, room and board, and give substantial financial aid.

Duke, in Durham, will charge $34,416 a year starting this fall. Davidson will charge $30,823, and Wake Forest, in Winston-Salem, estimates its fees at $30,280.

Hunter Rawlings III, the president of Cornell University, who led the effort to develop the new principles, said he expected other colleges and universities to sign on over the next few months, although he could not predict how many.

The new guidelines are part of a broad agreement by the 28 schools to continue to endorse need-based aid at a time when many states and colleges are increasingly offering scholarships to the students they want most - including athletes, those with the highest grades and underrepresented minorities - rather than those who most require financial aid to attend college. This approach is known as merit aid.

"There has been a gradual and accelerating erosion in the commitment to need-based aid," Rawlings said.

"Our group is trying to stop that erosion."

He said two factors behind the erosion were the strong competition for top students and a "lessened commitment to enabling low-income students to attend private universities."

The 28 colleges and universities also pledged to carry out the new policies consistently, so that there will be less confusion about the process and less suspicion about its equity.