Almost two-thirds of D.C. high school students questioned in a recent survey do not participate in any extracurricular activities, in most cases because they say after-school jobs keep them too busy.

An internal study of the D.C. school system's year-old rule requiring students to maintain a C average to remain involved in athletics or other activities shows that the rule has had little impact.

The report, prepared by the system's research office, also indicates that the rule has not been tightly enforced. The study, which included surveys of principals and 223 students in the 87,000-student system, shows that "up to a quarter" of students who reported taking part in an extracurricular program last year were not eligible to do so because their grades were too low.

But the study, which board member Eugene Kinlow (At Large) has been pressing the administration to release for more than six months, fails to answer the board's main question about the impact of the rule on the system's sports teams.

Instituted to cement the system's emphasis on academics, the C average rule was expected to have the most impact on athletics. But the report does not address that issue, because, it says, "little or no cooperation was received" from administrators and athletic coaches.

The school system's athletics program was severely criticized by an outside task force last month. Superintendent Floretta D. McKenzie then reassigned longtime athletics director Otto Jordan and the board pledged to improve and expand sports offerings.

But the new report questions whether students are interested at all in sports or other extracurricular programs. The survey found that 60 percent of students not involved in activities said they are not because of their jobs. About a quarter of nonparticipants said they simply had no interest. Only 15 percent of those sampled said they were not involved because of the C average rule.

Students who do join extracurricular activities most often choose sports. And most of the students who reported being involved despite being academically ineligible were on athletic teams.

"Up to 7 percent of the students . . . reported participating in sports and were ineligible," said the study, which did not discuss how those students got around the rule.

In general, the study found widespread support for the C average rule, from parents, teachers, administrators and students, about half of whom said the rule spurred them to work harder on academics. Many junior high schools have voluntarily adopted the rule. But the report says the system's effort to provide tutoring to students who are declared ineligible has been too little, too late.

A new tutoring program costing about $24,000 per high school did not begin until several months after the rule was imposed. And students and administrators alike do not seem to understand the link between tutoring and the ban on extracurricular activities, the study said.

In another matter yesterday, the school board decided to extend until the end of March the application deadline for candidates to succeed McKenzie as superintendent.

Board member R. David Hall (Ward 2), who is chairman of the search committee, told the board that the extra time will allow the committee to recruit candidates who have not applied.

"We are disappointed by the quantity of the applicants, not necessarily the quality," said board member Wanda Washburn (Ward 3). "The ads got out so late."

Although the board wanted advertisements for the position to run in national newspapers and education journals between Nov. 15 and Dec. 15, with a Dec. 31 application deadline, no ads ran until early December.

Only 47 persons have applied for the $85,000-a-year post, which McKenzie will vacate next month to become an educational consultant. No decision has been made on whether to select an interim superintendent or to rely on Deputy Superintendent Andrew Jenkins, who is nominally in charge in McKenzie's absence. Jenkins is a candidate for the top post.