On Yom Kippur, this Monday, schools in Montgomery, Prince George's and Howard counties will close, as they have on the Jewish High Holy Days for decades.

Elsewhere, on this day of atonement and fasting for Jews, public school classes will go on. In some counties, tests and special activities such as field trips are forbidden; in other places, it's business as usual.

Throughout the Washington area, public school districts' policies regarding religious holidays vary. Usually systems decide whether to declare a religious holiday a day off based on the size of a particular population affected and practicality--criteria affirmed in federal courts. But cultural sensitivity weighs too, and with the region's growing diversity, systems are faced with more requests.

"Everybody wants different things," said Bob Lazarewicz, executive director of operations in Howard County public schools. "What we've tried to do is compromise a whole host of competing interests."

Howard schools' student body is nearly 10 percent Asian, and residents who are Chinese, Korean and Vietnamese have asked that the Chinese New Year--a cultural holiday that involves games, ceremonial meals and visits with relatives--be an official day off.

In Fairfax County, Muslims, who make up an estimated 6 percent of the population, have been lobbying for several years to get the schools to forbid major testing on Islamic holidays, such as Eid al-Fitr and Eid al-Adha, and at the start of Ramadan, when children as young as 10 fast.

"For almost everyone, for the first three days you have a horrible headache," said Sharifa Alkhateeb, president of Muslim Education Council. "It is a very difficult few days--it would affect [children's] performance, that's for sure."

She acknowledged that planning tests and other activities around Islamic holidays, determined by the lunar calendar, can be difficult because they are set only after the sighting of the new moon.

Fairfax public schools spokesman Paul Regnier explained officials' reluctance to grant Muslims' and others' requests: "The question is, where do you start and where do you stop? You have Christians, Jews, Muslims, Sikhs, Buddhists. . . . We don't privilege one religion over another."

Typically, students are given excused absences on religious holidays, though teachers in most counties must use personal days if they want to take off. In general, officials say that until the numbers warrant it, schools won't shut down on such days as Ramadan or the Chinese New Year.

In Montgomery County, which has about 110,000 Jews, finding enough substitute teachers to work on religious holidays is impossible and arranging makeup work for so many students is a burden. So as a practical matter the schools close.

"We have so many students and teachers in our schools who are Jewish that it is hard to hold a school day," said Kate Harrison, a Montgomery schools spokeswoman.

Prince George's has fewer Jews, about 15,000, but the county schools' tradition of closing on Jewish holidays dates to when the Jewish community was larger.

No minority religious group in Fairfax is so large that its holidays cause major systemic inconveniences. About 300 of 12,000 teachers asked for religious leave last year on Yom Kippur, and the system tries to let teachers make up for religious time off without having to use personal days.

Fairfax schools do not close on religious holidays other than Christmas, nor do they forbid tests (as Prince George's and Montgomery do), because of the separation of church and state and the abundance of religions.

Most Virginia counties, including Fairfax, schedule spring break "when possible" to include Passover and Good Friday. Maryland law has mandated for more than a century that Good Friday and Easter Monday are days off. State Board of Education spokesman Ron Peiffer said the rule does not endorse the religious holiday but rather ensures a spring break.

The law was unsuccessfully challenged in 1997 by a Montgomery County teacher who said it was unfair that schools let off for Good Friday and Easter Monday while she had to use personal days for Passover. A judge ruled, in a decision upheld last month by the 4th U.S. Circuit Court of Appeals, that the days off are logistically, not religiously, motivated.

Ana Sol Gutierrez, a former Montgomery County school board member, favors a floating system of holidays, where students and teachers could take three days or so off as their worship and cultural rituals demanded.

"Now we have a huge diversity of students that don't necessarily follow the Jewish holidays," she said. " . . . Have Muslims do their holidays when it's their time; the Chinese, when its Chinese New Year; for Hispanics, the religious Catholic holidays."

No matter what, school officials say, there's no such thing as a perfect school calendar.