Today's Fourth of July activities begin at 10 a.m. with the annual Independence Day Parade down Constitution Avenue from Seventh to 17th streets. TV actor Mike Farrell will be grand marshal, leading 123 units with more than 4,000 participants.

Constitution Avenue between Seventh and 23rd streets will be closed for the parade between 9:45 a.m. and 1 p.m. Later in the afternoon, 17th Street between Independence and Constitution avenues will be closed in preparation for the fireworks.

At 2:30 p.m., the Jhoon Rhee Martial Ballet will kick off five hours of musical entertainment events at the Washington Monument, that will include the Jefferson County (W. Va.) High School Jazz Band; Tim Eyerman and the East Coast Offering; the United States Air Force's Tops in Blue, a 2-hour variety show; and The Grass Roots.

At 8 p.m., Mstislav Rostropovich conducts the National Symphony Orchestra on the Capitol's West Lawn. The concert will end just before the fireworks begin.

Fireworks begin at 9:15 at the Rainbow Pool by the Lincoln Memorial. The mainly aerial display, by Grucci, will be set to music and use 2,300 shells.

The National Park Service expects between 150,000 and 300,000 people on the Mall for the holiday event. Metrorail will operate on a Saturday schedule from 8 a.m. until midnight. Metrobus will operate an augmented Sunday schedule with extra service to the Mall on some routes. All fares are 50 cents.

Sunday traffic regulations will be in effect. Free parking will be offered at the Pentagon North parking lot, with free shuttle service to the Arlington Cemetery Metrorail station. Free parking will also be provided at all Metro lots.

In case of rain, the fireworks, the Grassroots and the NSO concert will be rescheduled for the same times tomorrow, July 5. If that happens, Metro service will be the same as planned for today.