As the last hours before Christmas ticked away yesterday, while the cash registers rang last sales and shoppers carried their burdens wearily or happily homeward, Washington was a kaleidoscope of seasonal ritual and remembrance, some of it startlingly new, some steeped in tradition.

It was an evening for a gesture to remember hostages held captive in Lebanon, a day for a married couple to make a romantic getaway in the full spirit of the season, a day that would end with the hint of snow and, for many, with prayer.

It also was a day in which the Christmas spirit of generosity would be symbolized by the landing of Santa Claus in a helicopter on one of the city's most hard-pressed streets. 'Twas the day before Christmas, not a snowflake in sight, and six children on Hanover Place NW were searching the sky for Santa Claus. A faint humming sound began, and in minutes it grew into a roar that could be heard for blocks.

Suddenly, a mighty wind lifted the sand from a vacant lot, knocked over trash cans and sent everyone scurrying for cover behind parked cars and boarded-up buildings. When the dust cleared, old St. Nick waved as he climbed out of a blue-and-white police helicopter.

The six children were quickly joined by 40 others who ran and skipped over to take part in what the District's Fraternal Order of Police called Operation Reindeer.

Together the FOP and the U.S. Park Police arranged for Santa to bring toys to children who lived in two neighborhoods, Hanover Place NW and Kenilworth and Eastern avenues NE, both notorious centers of heavy drug trafficking. Toys were given out to nearly 400 children in the program, according to a Park Police spokesman.

For Hanover Place, a one-block street near North Capitol Street and New York Avenue that police had once described as the center of the District's cocaine trade, Santa's high-profile arrival was the latest step in an effort to keep the drug dealers out of the area by maintaining high police visibility. The same helicopter that brought Santa had been used three weeks earlier as part of Operation Avalanche, which drove the drug dealers off Hanover for the third time in 18 months.

Many of the children in the neighborhood had come to fear the police as much as they feared the drug dealers. When a police officer working in the area tried to make a list of names and ages of the local children for yesterday's toy giveaway, some of the children gave false names and addresses.

Gary Hankins, a spokesman for the FOP, said the union donated $500 to buy food and toys for the children to demonstrate that the police do more than arrest people. "These kids didn't have a normal life style until we cleared out the drug dealers and pushers," said Hankins. "Now, we want to give them role models."

Santa (a.k.a. Officer John Kenner) said his visit to Hanover Place was special.

"It gives them something else to think about," said Santa. "It helps to give them a dream because it tells them they are special. How many kids can say that Santa came to see them in a helicopter that landed on their street?" -- Marcia Slacum Greene On the Ellipse, the lights of the National Christmas Tree were dimmed briefly at 6:15 p.m. as a gesture of respect and remembrance for the Americans held hostage in Lebanon and for their families.

President Reagan ordered the lights dimmed "as a gesture of respect in remembrance of our fellow Americans and their families," said assistant White House press secretary Mark Weinberg.

Weinberg quoted the president last night as saying, "While we dim the lights tonight, our hopes burn bright for their safe return to their loved ones."

Peggy Say, sister of Terry Anderson, one of the hostages, described the dimming of the lights as "at least an acknowledgment that we have accomplished something -- recognition" of those taken hostage and their circumstances.

"We've worked so hard for recognition," she said, according to United Press International.

Meanwhile, several Washingtonians noted with surprise last night that the light was lit in the lantern on the Capitol dome. They speculated that it was turned on specially for Christmas Eve.

Normally, according to a spokesman for the Architect of the Capitol, the light is lit only when Congress is in session. It was lit last night by mistake, he said, and was to be shut off. -- Martin Weil More than 5,000 voices soared, joyful and triumphant, toward the vaulted limestone ceiling of the Washington Cathedral last night at a Eucharistic service that warmed a cold and rainy Christmas Eve.

"Oh come, all ye faithful, joyful and triumphant, oh come ye, oh come ye to Bethlehem; come and behold Him, born the king of angels; oh come let us adore Him . . . "

Before the service, carillon hymns and carols -- from "Joy to the World" to "God Rest Ye Merry Gentlemen" -- prepped the standing room only crowd of families and friends that crowded into the nave of the elegant Episcopal cathedral and spilled into five surrounding chapels.

The service will be televised this morning at 9 on Channel 7. -- Victoria Churchville Late last night, forecaster Harold Hess, on duty at the National Weather Service office here, issued an unofficial and somewhat ambiguous prediction: At that time, he said, it seemed Washington was due for a "borderline white Christmas." He added: "It's going to be semiwhite, let's put it that way."

He said some overnight rain might be followed by a period of snow, with accumulations of perhaps an inch before cold, clear and blustery weather set in today.

Only traces of snow were detected early this morning. -- Martin Weil Yesterday was Gary and Rhonda Buyers' fourth wedding anniversary and the first Christmas Eve the Waldorf couple have had all to themselves. So they did what any head-over-heels-in-love couple with the same opportunity would do -- they opted for romance.

The couple's four children, from previous marriages, "are all out of town and we want to do something different for our anniversary and for Christmas Eve and Christmas morning, and we decided on a getaway," Buyers, 42, a furniture salesman, said in a telephone interview from the couple's room at the Grand Regent Hotel on M Street NW.

"Every now and then when we get a chance, we sneak away," Rhonda Buyers said, remarking that she was soaking in a luxury-size salmon-colored tub and sipping champagne as she spoke.

Christmas Eve was the Buyers' present to each other, they said as they prepared for a candlelit dinner at a downtown restaurant known for its strawberries dipped in dark chocolate. "It's very romantic and very nice," sighed Rhonda Buyers, a 35-year-old owner of an Washington employment firm.

And what's planned for Christmas morning?

"We're just going to relax, have breakfast and maybe take a long walk -- if it's not as cold as they say it's going to be," Buyers said. -- Victoria Churchville Those who gathered at midnight Mass at St. Mary Mother of God Roman Catholic Church came from near and far -- often from far. The church at Fifth and H streets NW -- known fondly as Old St. Mary's -- draws many worshipers from other parts of the city and from the suburbs, too. Joseph Scott, 74, said he was "born and bred" in the St. Mary's neighborhood. Now, Scott, a retired truck driver, lives near Georgia Avenue and Park Road NW. But he still comes to midnight mass. "It's a part of me," he said. Joyce Ames comes from Temple Hills to sing in the choir, and Jim Crytzer has come from Mount Vernon for about 10 years.

It is an old church in an old neighborhood, and Christmas Eve is not a night for forgetting tradition. -- Douglas Stevenson