For thousands of morning rush-hour commuters along the Capital Beltway, yesterday was a good day to just stay home.

Actually, there was very little commuting and not much rushing in the hours from 7:30 until after 10. A combination of traffic accidents and some untimely bridge repair work tied up traffic on almost the entire western section of I-495, from the Woodrow Wilson Bridge on the south to Georgia Avenue.

The best estimate was that more than 10,000 drivers were delayed, some for as long as two hours, according to Maryland State Police who were busy most of the morning fending off angry telephone calls. At one point, police said, traffic on I-495 northbound was at a virtual standstill for eight miles back, from River Road all the way into the heart of Northern Virginia.

The culprit for that pile-up, police said, was the driver of a 1978 Buick traveling south who decided to change lanes and lost control. The car went through the metal guardrail separating the two directions of traffic, causing a chain reaction involving three cars and a tractor-trailer rig.

Four people were injured in that pile-up, one, Harry Swan, 69, seriously enough to be hospitalized at Suburban Hospital in Bethesda for a fractured leg. Police said they were delayed for two hours in clearing up the mess because the truck trailer ended up resting on top of one of the cars.

That was at 7:30. Fifteen minutes later another tractor trailer hauling diesel fuel collided with a car on the eastbound, inner beltway loop just west of Georgia Avenue. That accident left diesel fuel spilled out over two lanes, and the Montgomery County Fire Department was called in to hose the highway down. State highway officials were also called in to put sand down to keep the roadway from becoming too slick.

But that wasn't the end. Shortly after 9:30, District of Columbia transportation department officials decided to block traffic at the Woodrow Wilson Bridge, to make some needed repairs on the bridge supports to keep them from vibrating. The whole process took 35 minutes, making a bad situation worse.

"It was a mess," said one police spokesman.

Maryland State Police in Rockville said their offices received several telephone calls from angry commuters who had been sitting on the beltway for two hours while it appeared that the troopers on the scene of the first trailer accident weren't doing much to clear up the accident.

But police said the problem was that the trailer became detached from the cab and rested on a car. Police and work crews on the scene couldn't move the trailer from the car, since they couldn't find anything better to rest it on.

Eventually, police said the trailer was removed by hoisting it by both ends using two tow trucks. The tow trucks held the trailer up, while workers removed what was left of the car underneath. The whole process took about two hours.

The four injured persons were taken to Suburban Hospital for various bruises.