Under drizzling skies yesterday, 359 years since the original feast was proclaimed at Plymouth Rock in 1621, many kinfolk, friends and strangers, hailing from far and near, joined in the city and suburbs of Washington to celebrate the last Thursday in November called Thanksgiving.

No matter the changes in the blunderbuss that kills the turkey or the late 20th century phenomenon of holiday football games, time has not substantially altered the essence of this annual rite.

But what about the holiday workers, the singles, the outcasts, the derelicts and the wayward with no clan or congregation, no opulent table of pies and sauces and basted fowl? For that matter what about the vegetarians?

To start, the nation's most prominent outcast, defeated President Jimmy Carter, did not lack for a traditional Thanksgiving, supping at Camp David on roast turkey, cranberry sauce, green beans, sweet potatoes, salad and pumpkin pie.

Carter also issued a proclamation, thanking the souls of Plymouth Rock for "the vision of brotherhood that is ours today."

But such a vision was a private affair for most. On a day in which all federal, state, county and city offices were closed, the streets of downtown Washington had a lonely, evacuated feeling as rain drizzled on and off and temperatures hovered in the 40s under a gray overcast. Snow flurries fell in western Maryland and other parts of the metropolitan area early in the day but tapered to light rain.

In the shadow of Rosslyn's modern downtown skyline, National Park Service ranger Phillip Jenny opened the gates to Roosevelt Island at 8:15 a.m. For a few singles strolling the gravel paths, it was a good way to lose the holiday blues.

There were half a dozen cars in the parking lot, and a few families traipsed the leaf-strewn woods where tall oaks wore pelts of ivy.

Jenny, a 41-year-old bachelor, spent most of the day reading in his tiny A-frame office, not minding that he had to work because he was earning time-and-a-half, and he had arranged a late supper.

Running ahead of their parents, two youngsters on a four-day holiday from Hyde Elementary School in Georgetown scampered through the waterless fountains at the memorial to Theodore Roosevelt on the 90-acre island. Jet engines overhead split the woodsy quiet. "The jets are my nemesis," Jenny said. "I lead walks, and I just have to stop talking until they're gone."

At the first Congregational Church at 10th and G streets NW, the crowds were bigger, attracted not by the tranquility of a stroll in the woods but by a Thanksgiving repast without the ubiquitous turkey. One hundred vegetarians, dedicated to the premise that "Thanksgiving is no treat for the turkey," turned out for potluck fare of beans, salads, fruits and meatless casseroles.

"It just seems that at Thanksgiving time vegetarians would feel very isolated if they didn't have a place to get together," said Larry Miller, 36, president of the Vegetarian Society of Washington, which sponsored the meal along with a group called People For Ethical Treatment of Animals.

Thanksgiving's traditional main course was not gladly missed at gatherings where dollars, not ethics, strapped the revelers. Many Washington churches struggled through the ageold task of feeding the poor.

"We were scared to death we wouldn't have enough, but we did what we could," said Rev. G. H. Jack Woodard, rector of St. Stephen & The Incarnation Episcopal Church at 16th and Newton streets NW.

Woodard and other groups that minister to the poor had earlier warned there might not be enough food for a task that seems to get bigger every year, but news of their difficulty brought last-minute contributions of food and money.

"We had more than 600 people we fed today, but we managed," Woodard said. The church closed its kitchens at 2 p.m. and sent its remaining supplies to another soup line.

Despite the charity, Thanksgiving with all its connotations was probably little more than an ironic afterthought for many of the city's down-and-outers, who prowled the deserted streets for castoff food. Even outside St. Stephen church, where dinners had been served, one couple groped through a trash barrel, looking for leftovers.

If there is a place where the past and the future are joined, it is the Smithsonian Institution's Museum of History and Technology, a place where 17th century pilgrims would be as much at home as today's architects of Rosslyn. It was there that Elizabeth Stanford, a Red Cross worker, was museum hopping yesterday with her daughter, Colleen.

"Only my grandmother makes a fuss about Thanksgiving," Colleen said, sitting down to a late lunch of chicken at the Smithsonian cafeteria, which never takes a holiday.

Elizabeth Stanford ordered turkey. She said she just liked it. "The holiday," she said, "is in the mind."