Accompanied by thunder, dark clouds and gusty winds, the heaviest rain in weeks fell in the Washington region yesterday, causing temporary flooding on key traffic arteries and contributing to numerous highway accidents, at least two of them fatal.

By late last night, 1 1/2 inches of rain had fallen at Reagan National Airport. High water covered all four lanes of the Capital Beltway's outer loop between Braddock Road and Route 236, restricting travel to one shoulder, said Virginia State Police spokeswoman Lucy Caldwell.

"It's pretty bad," she said.

About 8:30 p.m., traffic was backed up for three miles or so behind the flooded area, where water was about four feet high, Caldwell said. She said state transportation department crews were trying to clear drains so water could run off.

During one of the day's bursts of rain, standing water blocked the slow lane on Route 50 near Rowe Boulevard in the Annapolis area, said Maryland State Police Cpl. Mark Hurley. The torrent was "just too much for the catch basins," which were clogged by autumn leaves, he said.

Two teenagers died when their Jeep went out of control on a wet road and struck a tree, according to Montgomery County police. In the District, a teenager was killed when the car in which he was riding went out of control in Rock Creek Park, striking another vehicle. Park Police said that the rain probably contributed, but that an investigation was not complete.

Howard County authorities said a fatal accident occurred near Highland on a wet Route 108 yesterday morning.

According to National Weather Service meteorologist Jim Wiesmueller, yesterday's storm was produced, in part, by warm, moist air from the south at a time when a cold front was advancing from the north and west.

He said the storm brought lightning and thunder, neither of them common in late November, and a wind gust measuring 51 mph at Andrews Air Force Base. It "was basically a one-day thing," he said.

The coming week, he predicted, will be cool and dry.