It is 12:30 p.m., one of the five appointed times for daily prayer, and the leader intones the words of the prophet.

"La ilaha illa illa-llau" [There is no god but Allah], the leader cries in a voice that peaks and dips like the shifting sands of the desert.

"Muhammad rasul allahi" [And Mohammed is his prophet], the believers respond as they prostrate themselves.

It is a familiar scene throughout the Moslem world, but here there are some differences. The participants kneel, shoeless, on a wrestling mat instead of on hand-woven carpets. And their place of worship is a school gymnasium in Fairfax County, not a mosque in Riyadh.

They are students at the Islamic Saudi Academy, a kindergarten-through-sixth-grade school that opened its doors in August.

Founded by a decree of Saudi Arabian King Fahd and financed by the Saudi government, the school already has 350 students. "The government was concerned about their students who live here," Saad Adwani, the school's director, explained recently. "When they returned home they had problems with their language and their religion."

When teaching Arabic and Islam the school uses the curriculum of the Saudi Ministry of Education and textbooks are imported from Saudi Arabia. For all other subjects, the Fairfax County curriculum is used.

"The unique thing about this situation is that we combine these two curriculums in one school," Adwani said.

In the classrooms are pictures of mosques and minarets, and the school's flag is ablaze with verses from the Koran. "When you teach your Arabic language and your Islamic faith, that's when you teach your cultural heritage," Adwani said. "The culture is part of the faith."

The Saudi government at first explored the possibility of opening several schools in America, but found that idea impractical. The Washington area was selected as the site for a single school because of the large numbers of Arab business people, diplomats and American Moslems here. The 34-acre campus on Popes Head Road about 1 1/2 miles from George Mason University was purchased last year from the Fairfax Christian School, which closed but plans to reopen somewhere else next year.

Saudis make up 33 percent of the students, other Arabs 31 precent, American Moslems 29 percent and others 7 percent. Students of at least 11 nationalities attend the school, according to Adwani.

While a diverse student body has made the school possible, it also has presented the school's biggest problem.

"We have those who don't speak Arabic very well and those who don't speak English very well. We try to put them at different levels," Adwani said. All courses in English and Arabic are taught by native speakers. "

In a room that has a yellow construction paper sign demonstrating the use of the apostrophe ("Abdullah's brother is home"), an Arab and an American teacher discussed the problem.

"Teaching in a situation like this can be immensely rewarding if you can overcome the frustration of having 10 kids in front of you who can only say 'pencil sharpener,' " said E.J. Breltich, an American woman who teaches English to speakers of Arabic. Her Arab counterpart, Khalil Tahrani, agreed.

Both teachers said they believe that the school will overcome the problem within a year. "The school will provide any instructional materials we ask for," Breltich said. "That is a big plus. It is not like that in public schools." Average class size at the academy is 16 students and tuition is $1,000 a year, though administrators at the school say that is supplemented by the Saudi government at a rate of $6,000 to $7,000 per student.

Tuition, Adwani said, is charged only to ensure the interest of parents in their children's academic performance and behavior.

And teachers' salaries at the school are "comparable to or better than area public schools," Breltich said.

The reasons parents give for sending their children to the school are as varied as the students' backgrounds. Mohammed Sultan, an Egyptian who works for the Kuwaiti Embasssy, has two children enrolled in the school, both of whom attended classes in Egypt last year.

"It was very convenient for them to continue their education at this school," he said, "to learn Islamic religion and Arabic and get the American education."

But religion and language are not primary concerns for all who send their children to the school. Frank Mashuda, who described himself as a "conservative Roman Catholic," enrolled his 5-year-old son in the school's kindergarten for what he considers "an element of excellence and a healthy moral environment."

"I was impressed with their total professionalism," he said recently. "My child has to learn Arabic, but I don't consider that a handicap."

It was Saudi money that bought the three buildings for the academy, which sit atop a hill overlooking the basketball courts and soccer fields of the campus. New buildings are planned to meet the academy's projected expansion to a high school, and later a junior college with dormitories for out-of-town students, Adwani said.

Linda Wilson, who lives near the school, said the school has presented no problems for the neighborhood. She said that some neighbors had "discussed inviting representatives of the school over, just to meet them."

In fact, a passerby might not even be aware that there's anything different about the school, except when the children's names are called out. Where else would you hear a teacher warn: "Don't jump in the mud, Mohammed!"