This fall, for the first time, the 14-year-old National Presbyterian School will have fourth-grade students along with its traditional nursery school through third grade.

The fourth-grade class, which will accommodate 20 students, is part of a "phased expansion" of the school's academic program, said Jane Bissett Harter, director of the church-operated school at 4121 Nebraska Ave. NW. She said fifth-grade classes will be added next year and grade six in 1985.

Harter said the expansion this year was made possible by a grant of $40,765, from the Morris and Gwendolyn Cafritz Foundation, which will pay for classroom furniture, books, special learning materials and equipment, teachers' salaries and certain administrative expenses.

Harter said the new grade four curriculum, "will emphasize enhanced science, art and music programs in addition to NPS' traditional primary emphasis on English, mathematics, social studies and French." Comparative religion, enriched history and geography are among other courses planned for fourth through sixth grades.

Suzanne Richey, whose son Dugan MacVaugh will be one of the first fourth graders, said the expansion is "a good and necessary idea because there are not enough quality places for kids in the Washington area."

Although the school was founded by members of the historic National Presbyterian Church, its 150 students, whose tuition this year will be $2,835, represent a number of faiths. About 70 percent (105 of 150) of the students are from the District; the rest are from Virginia and Maryland.

During its first three years, the school developed a nursery program for 3- and 4-year-old children. In response to parental and community demand, it established its first kindergarten classes in 1972. By 1975, classes through third grade had been developed.

"But before this growth was completed, it became evident that continued development of a quality education program would produce a larger student body and staff that soon would exceed the space of the school," Harter said.

She said the school has a growing waiting list and parents want the school to expand its program through the sixth grade--"the logical end point for an elementary program."