Unusally heavy rains early yesterday forced the closing of one elementary school and flooded several roads and numerous basements in what residents said was the worst summer storm in years to hit the Lanham-Seabrook area of Prince George's County.

The downpour began about 6 a.m. and continued for three hours, according to Capt. James Mundy of the county fire department, which received more than a hundred calls of flooding as deep as six feet in some basements. While scattered showers occurred elsewhere in the Washington area, there were no other reports of major flooding.

"It was about as intense as I've ever seen a storm," said Mundy, who also lives in the area. "Fortunately, we don't have a basement."

During the storm and until midmorning, Mundy said, major thoroughfares were clogged by water and there was one report of a family stranded inside a car on Lanham-Severn Road near Glenn Dale. One fire station suffered from a leaky roof, but service continued without interruption.

Flooding in the basement of Seabrook Elementary School interrupted the first day of school for some 350 youngsters who were sent home about 10 a.m. when rising water in the basement caused officials concern over the building's electrical system. Gaywood Elementary, Thomas Johnson Middle and DuVal Senior High School, all in the same area, also reported flooding but remained open.

Meteorologist Edward Schoenberg of the National Weather Service estimated as much as two inches "and possibly more than that" fell in the localized downpour he described as typical of summer storms in this area.