When some students report to class in the District of Columbia Wednesday, they may be asked an unusual question: If a teen-ager wants to wear a Ku Klux Klan button to school, is that student protected under the U.S. Constitution?

The answer: The button symbolizes free speech guarded by the Constitution's First Amendment, but courts have restricted such expressions if they would disrupt a school or interfere with individual rights.

The question is drawn from a sample lesson for a teach-in that will be held in District schools Wednesday as part of the observance of the bicentennial of the Constitution, which was signed in Philadelphia 200 years ago Thursday.

Although national attention will be focused primarily on the big events in Philadelphia, many local celebrations have been planned, including "A Celebration of Citizenship," Wednesday's nationally televised extravaganza that includes President Reagan leading the Pledge of Allegiance from the Capitol steps. Thousands of area schoolchildren will be bused in for the event, and federal officials have encouraged agencies to give their workers 90 minutes of leave time to attend.

Some suburban jurisdictions plan to dedicate plaques at historic sites or emphasize the Constitution at local fairs.

In contrast to the 1976 celebrations of the bicentennial of the Declaration of Independence, the overall tone of the current commemoration is more subdued and diffuse.

"The declaration was more of a birthday party," said Jill Brett, a spokeswoman for the National Archives, which houses both documents. "This is probably more of an observance and less of a celebration. The Constitution is more of a weighty document than the declaration. The declaration was a call to arms. The Constitution . . . was a symbol of order."

A week of local events observing the bicentennial begins today at the National Archives, which will keep open its rotunda for 87 continuous hours, beginning at 6 p.m., for viewing of all four pages of the Constitution. Usually all four pages are put on display only one day a year.

Music and speeches will begin on the Archives steps at 4 p.m. today, and music and drama will be performed during the next three days.

This week's second major event will be the "Celebration of Citizenship" on the West Lawn of the Capitol Wednesday, described by organizers as a "star-spangled salute to the United States Constitution." Underwritten by corporate donations, it will be sponsored by the Commission on the Bicentennial of the United States Constitution, headed by retired chief justice Warren E. Burger.

The program begins at 11:30 a.m. with school bands, speeches and dramatic performances. The televised portion of the program, including the president's pledge, speeches by congressional leaders and a reading of the Constitution's preamble by Burger, will be broadcast from 1:30 to 2 p.m.

More than 16,000 students from 180 area schools will be bused in for the event, and thousands more will watch the broadcast in their classrooms. Many schools also will hold teach-ins on the political and social issues posed by the Constitution.

In the District, more than 100 lawyers and public officials, including Cabinet officials, former senator Randolph Jennings (D-W.Va.), D.C. Council member Jim Nathanson (D-Ward 3) and three members of the District Board of Education, will visit public school classrooms to lead lessons on the rights guaranteed by the Constitution.

In elementary schools, a suggested lesson on due process includes a discussion of the Salem witch trials. In high schools, suggested lessons focus on free speech and student rights: May a student newspaper publish an interview with a teacher about homosexuality, for example?

"We want kids to do their own thinking, rather than memorize the preamble," said Peter deLacy, program director for the D.C. Center for Citizen Education in the Law, a sponsor of the teach-in. "We want kids to think about the Constitution and how it applies to them."

At Robert E. Lee High School in Springfield, 25 politicians, lawyers and others, including the Fairfax County sheriff, will speak to classes about issues such as civil rights and separation of church and state. They will also touch on areas "where the Constitution has failed," such as the World War II internment of Japanese Americans, according to Glenna Terrell, a George Washington University graduate student helping coordinate the event.

Weather permitting, the 350 pupils at Little Run Elementary in Fairfax plan to make a human map of the United States on Thursday afternoon on the school ball field.

Other local events Thursday include a noon concert by the U.S. Army Field Band and Chorus at the Archives, and a 1 p.m. concert at the Jefferson Memorial by the 600-member Mormon Youth Bicentennial Chorus.

In Prince George's County, the government's bicentennial commission took a unique step: It sent letters to 400 ministers encouraging them to preach sermons about the Constitution today. One potential topic, the letter suggested, is the mandated separation between church and state in which neither is supposed to interfere with the other.

Commission Chairman Van Caldwell rejected suggestions that the letter might constitute official interference. "They don't have to," he said. "They can turn us down if they like."