The sun, which played hide-and-seek with Washington for much of the Memorial Day weekend, stayed out for several hours yesterday afternoon and the result was immediate and overwhelming: tens of thousands of picnickers flooded the region's parks with cars and charcoal grills in such large numbers that there simply was not room for everyone.

U.S. Park Police repeatedly were forced to close East Potomac and Anacostia parks in the District of Columbia, Fort Washington and Carderock parks in Maryland, and Fort Hunt in Virginia in an effort to cope with the crush of people.

As some of the picnickers left, the police let more people in so they, too, could join in the American holiday tradition of eating roasted hot dogs, hamburgers and fried chicken, and getting a sunburn to remember it all by.

East Potomac Park was so crowded with Memorial Day celebrators that when deacons from the Guiding Light Full Gospel Baptist Church in Southeast Washington showed up at 6 a.m. to claim a few picnic tables for a church picnic, they found the ones they needed were already taken. Nonetheless they managed to talk a few people into giving up their tables to the church group.

Police at the park seemed to have all they could handle trying to keep the inch-along traffic moving so they ignored the hundreds of cars parked illegally on the grass at the park, which separates the Potomac River and the Washington Channel at Hains Point. In all, several park policemen said it was the busiest Memorial Day in the Washington area in several years.

While most of the picnickers seemed oblivious to observance of the holiday itself, several thousand people did visit Arlington National Cemetery to pay tribute to the nation's war dead. Some listened to a speech by Defense Secretary Harold Brown, while others watched as an Army officer placed a wreath at the grave of President John F. Kennedy. Yesterday would have been the slain chief executive's 61st birthday.

The throngs were not limited to National Capital parks. More than 25,000 people packed their way into the Needwood Lake park in Montgomery County, according to manager Jack Drinon.

He reported that the park's 40 rowboats, 15 paddleboats were all rented by noon, three hours earlier than is often the cast on a holiday or weekend. One reason might have been the fishing: Drinon said that bluegills, crappie, catfish and bass were biting yesterday.

David Jones, a park ranger at the Great Falls Tavern on the C&O Canal, said the parking lot there was filled to its 693-car capacity yesterday after being only half full Saturday and Sunday.

"It typical of every Memorial Day weekend," he said. "People stay home on Saturday and Sunday or go to the beach and come to the park on Monday."

But thtre was at least one indication that many Washingtonians, faced with drizzly rain and fall-like weather at the Atlantic Ocean beaches, did not leave town.

Nearly 10,000 fewer cars traveled across the Chesapeake Bay bridges on Friday, Saturday and Sunday this weekend compared to last Memorial day.

The weather also had a noticeable effect on shoppers. Peter Conit, a security guard at Montgomery Mall, noted that when the skies were overcast and a bit menacing yesterday morning, there was a large crowd at the shopping center.

Then the sun came out, and it was bye-bye shoppers.

No matter what the park yesterday, the emphasis definitely was on eating, then eating some more. And then more still.

Johny Cox, a 35-year-old tractor-trailer driver, stood near the polo field in West Potomac Park cooling 10 pounds of hamburger and fistfuls of hot dogs on a 55-gallon drum that he had fashioned into a barbeque grill.

"We come here every holiday, in fact just about every weekend," Cox said. "The kids play softball and football and the adults just sit around and talk."

At Hains Point, Edith Lewis, whose husband Willie J. Lewis is the pastor of the Guiding Light church, said simply, "We eat all day and everybody goes from table to table sharing.

"Because most of us are from North Carolina," she said, "we had collard greens and cornbread dumplings. And we had peas, rice and some kind of coconut juice."

For the members of the Guiding Light church, the day's festivities end with singing and a prayer. Often, she siad, other picknickers join in with them before calling it a day and packing the kids, the grill and the leftovers - if any - into the family car.