Almost two inches of rain deluged parts of the Washington metropolitan area yesterday, causing minor flooding in isolated sections and helping to create a massive traffic tieup on the Capital Beltway in Fairfax County where diesel fuel spilled on the wet road.

Showers, some accompanied by lightning that caused scattered power outages, fell intermittently through the humid day.

The rain's intensity peaked in late afternoon when more than three-fourths of an inch fell near downtown Washington in less than 20 minutes.

Cars stalled in rising water in the westbound lanes of Independence Avenue at 17th Street SW as rain appeared to overwhelm catch basins, according to the U.S. Park Police.

High water also forced the closing last night of Hains Point and some of the side roads in Rock Creek Park.

Basements flooded throughout Charles County, while high water covered parts of some side roads, reported Lt. John L. Brown of the sheriff's department.

Fountains of water spouted from manholes, leading to numerous but inaccurate reports of water main ruptures, he said.

Spawned by meteorological conditions that have been affecting weather over much of the Atlantic seaboard and southeastern United States, yesterday's rain amounted to 1.87 inches by late last night and brought the total for the month to 3.62 inches, according to forecasters.

Rainfall for September usually averages 3.22 inches.

The rain was blamed last night by a Virginia Transportation Department official for difficulties encountered in cleaning up a spill of diesel fuel that shut down the inner loop of the Beltway west of the Van Dorn Street exit starting shortly before 7 p.m. All lanes reopened shortly after 11 p.m.

In the Beltway accident, a tractor-trailer was struck by a car that had attempted to pass it on the right shoulder, according to Fairfax County police.

One of the cars on the trailer broke loose, and about 100 gallons of diesel fuel were spilled from the tractor-trailer after it jackknifed.

Efforts to spread sand to absorb the spill were hampered by the rain, said Transportation Department spokeswoman Marianne Pastor.

All four lanes of the Beltway were shut behind the site of the accident, about half a mile west of the Van Dorn Street exit, Pastor said.

"It has caused us some considerable traffic problems," she said.

Lightning that accompanied the 4 p.m. cloudburst was blamed by a Virginia Power spokesman for cutting off electricity for a time to about 2,000 customers in parts of Alexandria near Rte. 1 and Quaker Lane.

A spokeswoman for the Potomac Electric Power Co. said the storm knocked out power to about 2,000 of the utility's customers, scattered through the District and Montgomery and Prince George's counties.

National Weather Service forecaster Scott Prosise said showers and thunderstorms, generated by the combination of moisture flowing from the Atlantic, a cold front pushing eastward and disturbances aloft, are expected to persist throughout today and to dissipate late tomorrow.