WASHINGTON (AP) _ Howard University students have agreed to contribute $15 apiece to the school's endowment each semester to raise about $2.5 million in four years and to underscore alumni support.

Howard spokesman Henry Duvall said the Independence Initiative was approved by the university Board of Trustees during the weekend with the endorsement of student leaders, the student newspaper and respondents to a student survey.

''We believe that this may be the first time that students have ever sponsored such a fund-raising initiative,'' said M. Kasim Reed, Howard's undergraduate trustee, who developed the idea. He said ''it sets an example for the nation's other colleges and universities to follow.''

Beginning this fall, in addition to tuition - $5,825 for 1991-92 - and other fees, all Howard students will pay a $15 surcharge each semester.

Reed said conservative estimates are that the Independent Initiative will generate $139,500 in the first semester. The federal government has a special matching fund program that is expected to contribute $279,000 to the university's endowment funds.

Duvall said the endowment fund, as of June 30, 1990, was at $84.5 million. Officials of the university's office of the vice president for business and fiscal affairs-treasurer, said that in four years, about $2.5 million will be generated for the endowment fund through the surcharge.

Under the initiative, half of the earned interest income will be available for student financial aid and academic programs.

Reed, 21, a political science senior from Atlanta, said he first thought of the idea in 1989 while working as a student intern in the office of Rep. Joseph P. Kennedy II, D-Mass. He presented the plan to university President Franklyn G. Jenifer, and then to other administrators and student leaders. ''The thrust of the program is to recognize both the importance of Howard University's being a strong institution and the relative independence that comes from having a substantial endowment,'' said Reed.

With the Independent Initiative, Jenifer ''will now be able to tell Congress that Howard's future alumni are behind the university 100 percent,'' said Reed.