The Washington area woke up to a bright spring day yesterday of sunshine, mild temperatures and light breezes. It was a day that coaxed thousands of area residents to go out and take a walk.

And walk they did, all over the metropolitan area. In the District, some people strolled along the Mall or around the monuments, while others down the towpath by the C&O Canal.

In Virginia, hundreds of people went walking for charity, earning a few more cents for their cause with every step they took. And in Maryland, an estimated 50,000 people took a walk across the Chesapeake Bay Bridge.

It was the fourht annual Bay Bridge Day yesterday the day when one span of the graceful William Preston Lane Jr. Memorial Bridge was closed to cars and open to those on foot.

And this year, the four-miule walk across the bridge was far more popular than its organizers had expected - more popular, in fact, than it had ever been before.

Richard League, the superintendent of the bridge, had expected about 35,000 people to come out for the crossing. But when the first buses arrived to take people to the bridge at 9 a.m., long lines had already formed in the designated parking areas where bridge walkers were to leave their cars.

The parking losts were full by 1:30 p.m. and had to be cclosed, although the Maryland Transportation Authority had listed 3 P.m. as the last time to catch a ride to the bridge, league said. About 30 busloads of eager pedestrians were still waiting to go the bridge from at least on location when the lots were closed, he said.

League attributed the big turnout to the beautiful weather and to the facat that people "have been caged up all winter." The walk is one of the first spring activities available, he said.

Although a few walkers grumbled and said they spent as long waiting for buses as they did walking across the bridge, the crowds were orderly and well mannered. People chatted with their neighbors in line, bought the kids ice cream cones, and listened to ball games on the Radio. One man even brought his guitar and played folk songs.

But what would possess 50,000 people to walk over the bridge, an event that some of the traffic supervisors called "crazy"?

"It's a fascination to walk across the bridge, something you can't do the rest of the year" Sgt. Robert Werner, of the Thansportation Authority, said.

As far as Clement and Harnet Shugerman were concerned, "It sounded like a good thing to do with the kids," Mrs. Shugerman said. "We've driven over the bridge many times and there's a lot of nice scenery we normally can't see."

The crowds didn't bother the family who had driven out from their Washington home because, Mrs. Shugerman said, "it will make it more fun because you can people-wattch." The most important thing to 3-year-old Jed Shugerman, however, was seeing the host of sailboats that dotted the water.

Even as the day became slightly overcast people continued to enjoy their stroll. Stephanie Schultz of Baltimore said she came to the walk because it "start of spring" and "you can only do this once a year."

Some of the hikers said they found the walk across the bridge a challenge. But for Elizabeth Lay, a grandmother from Brooklyn Park, the challenge was not nearly that difficult.

She proudly told a reporter that she passed up the rest of her familyu, including her grandchildren, and was patiently waiting for them to finish. "I've been here a half hour waiting for them and they're all younger that I am," she said.

The happiest people on the crossing seemed to be the children - until they grew tired, that is. Most of them began the excursion with the exuberance of youth but by the end many parents were tending to sore feet and were cajoling their offspring to finsih by reminding them of the ice cream cones at the bust stop.

"My feet are tired," said young Glenn Fitzpatrick who had come with his family from Lexington Park in southern St. Mary's COunty. His younger brother Drew, however had one found memory of the walk. The best part, he said was "throwin my gum on the boat."

Meanwhile in Northern Virginia, thousands of people, mostly children, joined the Walk for Mankin. And this year, in keeping with the country's move to metric measurements, walked 32 kilometers (about 21 miles) rather than the 20 miles the ocurse have run in the past.

According to Wyatt Durrette, a Vienna lawyer who has been active in promoting the walk since it began in 1970, local Jaycee groups sponsored the eight local charity walks.

Durrette said he did not know how many people participated in the "grueling" walk, but he estimated that the groups raised a total of $100,000. The money is donated to Project Concern, Inc., of San Diego, a non-profit medical-dental assistance organization founded 17 year ago, he said.