Metro will operate the subway and some special bus service Tuesday to accommodate persons watching the July 4 fireworks display on the Mall. Then everybody will get a free ride home.

Regular nonrush-hour traffic will be charged on both bus and subway until 9 p.m. After 9, all rides will be free.

Metrobus will operate a normal Sunday schedule all day Tuesday, but will augment that schedule with extra service on key arterial routes beginning about 4 p.m. and running through the evening.

Subway riders will get to take advantage of Metro's new nonrush fare of 50 cents for all trips regardless of distance until the free rides begin at 9 p.m. Farecards must be used for the 50-cent trips. The fare gates will be locked open at 9 p.m.

Free parking will be provided at all Meto-operated parking lots and at the Montgomery County parking lot near the Silver Spring station. However, drivers must pay the standard parking fee at two othe rlots - $1.25 at the RFK Stadium lot near the Statium Armory station and $1 at the lot adjacent to the Pentagon City station.

The Pentagon north parking lot will be free and free shuttle buses will carry riders from there to the Arlington Cemetery Metro station.

Metro officials have asked that persons gathered on the Mall to watch the fireworks walk to any one of several stations in the Mall area after the display instead of all trying to reach the Smithsonian station.

Montgomery County's Ride-On minibuses will operate on Sunday schedules from Broadmore, Wheaton Plaza, Dennis Avenue, Takoma Park and Langley Park. Extra service to the Silver Spring Metro station will be provided from Rosemary Hills and White Flint beginning at 9 a.m. Free rides will begin at 9 p.m.

Additional information about Metro bus and subway service can be obtained by calling 637-2437. For more information about the Montgomery County Ride-On, call 468-4100.