The first of the holiday revelry had just begun in parks and backyards throughout the area yesterday, when the sky opened and dropped a stormy, wet blanket on the three-day holiday.

Besides drenching picnickers and spoiling other outings, the storm front spawned a small tornado that touched down in Hillcrest Heights, and the rain caused an 8-car accident on the Beltway.

Prince George's County police said the twister hit in the 4100 block of Blacksnake Drive in Hillcrest Heights at about 3:45 p.m. No one was injured, but police said that several homes were damaged by falling tree limbs, and the roof of an unoccupied house was partially blown off.

Potomac Electric Power Co. reported that 200 customers in the Hillcrest Heights area lost power for about three hours because of the tornado.

About the same time the tornado struck, two cars went out of control in the rain and struck the median of the Beltway near Rte. 450 in New Carrollton.

Maryland State police said that while the drivers were trying to extricate their cars, a tow truck, which swerved to avoid hitting them, hit another car, causing a chain reaction. Police said eight vehicles were involved in the pile up, and one car flipped over overturned.

Four men were admitted to Prince George's County Hospital for treatment, hospital officials said. They were all listed in stable condition last night.

Hospital officials said two of the men have minor internal injuries; one man has a fractured spine and a fractured right arm. The fourth man had no apparent injuries, but was admitted for observation.