WASHINGTON — The College Board, publisher of college-preparatory exams, is auditing every high school Advanced Placement course in the nation, asking teachers of an estimated 130,000 AP courses to furnish written proof by June 1 that the courses they teach are worthy of the brand.

An explosion in AP study — participation in the program has nearly doubled this decade — has bred worry, particularly among college leaders, of a decline in the rigor for which the courses are known. Once the exclusive province of elite students at select high schools, AP study or its equivalent is now more or less expected of any student who aspires to attend even a marginally selective college.

The number of Hawai'i public school students taking AP exams increased 13.2 percent between 2005 and 2006, according to the College Board, which oversees AP curriculum and administers the three-hour AP exam.

Since 2001, the number of exams taken by Hawai'i public school students has increased by more than 63 percent.

In the haste to remain competitive in the AP arms race, schools sometimes award the designation to courses that barely resemble the college curriculum the program is meant to deliver, according to College Board officials and educators. Until now, there has been no large-scale effort to weed out such abuse.

Beginning with the 2007-08 academic year, only teachers whose syllabuses have been approved by the College Board may call their courses AP. Each teacher must submit an audit form, along with a syllabus for the course he or she teaches. Depending on how well the teacher's syllabus — assuming he or she has one — reflects the rigor expected by the College Board, the process can be brief or time-consuming.

The task has been met with no small amount of grumbling. But many faculty begrudgingly accept that some quality control is needed, lest the AP program spiral out of control.

The implications for high schools and colleges, students and teachers are enormous.

One would be a probable decline — after years of double-digit growth — in the number of courses labeled Advanced Placement. College Board officials have set a goal of approving at least 105,000 AP courses, of an estimated 130,000 nationwide. The attrition, they predict, would come mainly from teachers who decline to participate. No school will be restricted from giving the exams, although students without adequate preparation are unlikely to take them.

Tom Matts, a College Board official who oversees the audit, said its purpose is to help teachers elevate their courses.

"We're not trying to eliminate any courses," he said, "but to help teachers understand what needs to be in the course and to provide evidence in the syllabus" that college-level material is being taught.

Since its Jan. 23 launch, the audit has drawn submissions from 55,000 teachers, Matts said. University professors review the courses and usually respond within two months. Seventy-four percent of courses have been approved to date.

Unsuccessful teachers are encouraged to resubmit up to three times, with guidance from the College Board. Once approved, teachers and their syllabuses are sanctioned until they move to another school or the course requirements change.