The SAT, the most widely used college entrance exam for generations of students, is getting a makeover.

David Coleman, president of the College Board, which creates and administers the SAT, e-mailed his 6,000 members on Tuesday to inform them that the board will redesign the test to more sharply focus on the “core set of knowledge and skills” that high school graduates need to succeed in college.

In his brief message, Coleman called the project an “ambitious endeavor” but did not provide details about why the College Board wants to change the exam, how long it will take or what the process will entail.

Coleman, through a spokesman, declined to comment Tuesday.

The overhaul comes as the SAT is starting to lose market share to a rival standardized exam, the ACT. Historically, the ACT has been taken by high school students in the West and the South, while those on the East and West coasts have tended to take the SAT.

More than 1.66 million students in the class of 2012 took the SAT, making it the largest class of SAT takers in history. And the pool of test takers has become increasingly diverse, with rising numbers of low-income, African American and Hispanic students taking the exam.

But in 2011, the number of students who took the ACT surpassed the SAT for the first time, and Coleman suggested in his e-mail that one reason for the makeover is to ensure that the SAT is relevant.

“While the SAT is the best standardized measure of college and career readiness currently available, the College Board has a responsibility to the millions of students we serve each year to ensure that our programs are continuously evaluated and enhanced, and most importantly respond to the emerging needs of those we serve,” Coleman wrote.

He wrote that his objective is to increase the value of the SAT to students, higher education officials, and to K-12 administrators, teachers and school counselors.

As soon as Coleman became president of the College Board in October, he said the SAT could be improved. Before joining the board, he helped write the Common Core standards in English for kindergarten through grade 12 that have been adopted by 46 states and the District. The new standards will be rolled out by 2014.

Coleman has said the SAT should be more closely aligned with the new standards, to better connect the test to the kind of academic work expected of students in high school and college.

The SAT was last revamped in 2005, when a written essay was added, the test time expanded and the total possible score raised from 1600 to 2400, among other changes. Coleman has been critical of the essay, suggesting that it allows too much personal narrative and doesn’t challenge students to make evidence-based written arguments, a skill demanded in college.

A top official at George Mason University, where the SAT is accepted but not required, applauded the College Board announcement.

“I view this as a very positive step,” said Wayne Sigler, vice president for enrollment management at George Mason. “The College Board is aware, I think, of the need to continuously work to improve its product.”

But some college admissions leaders like the SAT more or less as it is.

“From where I’m sitting now, we’re not clamoring for them to change it,” said Charles Deacon, dean of undergraduate admissions at Georgetown University. “We still happily use the SAT. We’ve found that the test is predictive. There’s a lot of value in it.”

Georgetown accepts the SAT and the ACT, and many applicants submit both scores, Deacon said.

Henry Broaddus, dean of admission at the College of William & Mary, which accepts both the SAT and the ACT, said the school is “a satisfied customer with the SAT.” Efforts to improve it are fine, he said. “But I would not say that indicates a need for radical change.”

Valerie Strauss contributed to this report.