The old year took a limousine ride into history last night as New Year's Eve celebrants, decked out in black ties and blue jeans, took to the streets of Washington to welcome 1986 with a stylish but raucous celebration.

With only seconds left in 1985, D.C. Mayor Marion Barry and his wife Effi led a crowd estimated by police at 100,000 in the countdown as a 900-pound copy of the 1986 "LOVE stamp" descended from the clock tower of the Old Post Office Building on Pennsylvania Avenue. The huge, jostling crowd cheered "Happy New Year!" amid the muted popping of champagne corks and an unruly chorus of tooting horns.

The event, dubbed "Putting on the Glitz in 1986," was part pep rally and part rite of passage. The mayor and his wife, taking the stage with D.C. City Council Chairman David Clarke, drew a strong response when Barry shouted, "Let's hear it for Washington, D.C., Washington, D.C."

The Grucci Brothers fireworks erupted in rapid-fire, echoing sharply down the concrete corridor formed by the buildings on Pennsylvania Avenue. And then came the slightly boozy version of "Auld Lang Syne" that signaled a new calendar year.

While good cheer was in the air, a sense of near-pandemonium also pervaded the densely-packed crowd at times when celebrants discovered it was nearly impossible to move in the gridlocked human mass.

Police officers, dispersing small fracases in various sections of the crowd, sliced their way through the throng Conga dance style to reach the disturbances.

Police made 11 confirmed arrrests for disorderly conduct, and reported several minor injuries resulting from broken glass in the street, said Lt. William White III. About 9:30 p.m., police dispersed a group of 30 to 40 teen-agers who were fighting at 11th Street and Pennsylvania Avenue. No arrests were made in that incident.

Another kind of celebration was going on, meanwhile, in the delivery room at Greater Southeast Community Hospital in the District, where at 12:01 today an 8-pound 8-ounce baby girl was born, apparently the first in the Washington area this year.

A spokeswoman for the hospital said the gray-eyed, black-haired baby, who had not been named early today, and her mother, Toye Ford of 801 Bellevue St. SE, were in "excellent" condition and resting comfortably.

Not to be outdone, Holy Cross Hospital in Montgomery County reported that twin girls, Kristina Marie and Karen Ann, were born at 12:31 and 12:32 a.m. to Stanley and Linda Haley of 8655 Pioneer Dr., Severn, Md. A nurse at the hospital said the delivery room was "very crowded. Everybody wanted to be in on it."

At least two more persons missed the downtown festivities so they could be married at the Fountain Memorial Baptist Church in Southeast Washington in a 12:02 a.m. ceremony. John Hummel, 35, and Rita Watts, 31, were one of the first couples in the area to be married this year. Hummel, a certified public accountant for the firm of Peat, Marwick, Mitchell & Co., and Watts, an illustrator for a local defense contracting firm, said they plan to make their home in Alexandria.

"We think it was just a nice idea to bring in the New Year with a new life," Hummel said after the ceremony. "Besides, it's also a good way to remember our anniversary."

Delaware's lone House member, Rep. Thomas Carper, also celebrated the new year by getting married in New Castle, Del., in a ceremony that began shortly after midnight.

The two-term Democrat wed Martha Stacy, 36, an employe of the Du Pont Co. It was the second marriage for Carper and Stacy's first.

Back at the New Year's Eve celebration, standing at the fringes of the crowd, was Old Father Time, played by Navy Chief Petty Officer Jerry Foley. Dressed in a robe, with a beard and long, flowing wig, Foley said he thought Father Time should be represented at the festivities and he was the man to do it. "People have been pulling on my hair all night," said Foley, posing for photographs with teen-aged admirers. "I've been mistaken for Jesus Christ and Hare Krishna -- but most people know who I'm supposed to be."

This, Washington's third celebration, with each year's crowd increasing, drew a wide cross section of area residents and attracted many of the city's leading lights in the political and business arenas.

At a second floor reception held by Barry inside the Old Post Office Building, political insiders and others hobnobbed and drank champagne -- among them City Council member Frank Smith, who said the New Year's Eve celebration was a clear indicator that the city is on the rise.

"I think the spirit we see here tonight and the excitement are something we have to preserve," Smith said.

Partygoers taking to the wheel stood a chance of running into police officers around the metropolitan area interested in testing their breath, not toasting their health.

"We are running a double alcohol enforcement program for 16 hours. That's the first time we've done this," said Capt. David Baker, head of the D.C. police traffic branch.

Twelve officers and three sergeants were assigned to work the alcohol enforcement program, which started at 8 a.m. yesterday and will run through today.

During that same period last year there were 41 drunk-driving arrests in the District. Baker said he thinks more people are aware of stiffer drunk-driving laws and will ask others to chauffeur them home.

As of midnight, officials said about 20 people had been arrested in the metropolitan area on drunk-driving charges.

Earlier in the evening, the mood downtown was a mixed bag, with some partygoers expressing doubt that the crowd would reach the 100,000 estimate.

Vendor James Lodges, who was selling James Brown T-shirts and party hats, said he would not be doing business at the Old Post Office Building in the coming years.

"This will be the last one," said Lodges, standing in a light drizzle that appeared to dampen the turnout in the earlier hours. "Where are the 100,000 they talked about?"

A hard rock beat blasted from the stage and across the street from Lodges, where another vendor, Grover Price, said he was selling hats like hot cakes. "Last year I watched New York on TV with my girlfriend, but my girlfriend quit me, so that's why I'm working. Maybe next year I'll have another girlfriend and I won't have to sell hats."

The smells of smoked sausage, popcorn and hot dogs filled the air, along with the unmistakable odor of beer.

At the party inside the Old Post Office Building's Pavilion, Cab Calloway was the headliner, pulling the strings of nostalgia with his hi-de-hi-de-hi-de-hi, hi-de-hi-de-hi-de-ho routine, while the "Godfather of Soul," singer James Brown, brought his brand new bag of old tricks to the outdoor stage, where at midnight the famous Ditchley Bells would toll the new year.

City officials, led by Barry, hailed the party as a rival to New York City's annual bash at Times Square.

"Times Square has more of a history, tradition, but we're gaining on them," the mayor said. "We're going to outdo New York. We think we might just take over and become the best single event."

This new ritual in the federal capital coincided with the annual event in New York City that features the lowering of an apple symbolizing the traditional home of America's New Year's Eve celebration.

There, New York's Mayor Ed Koch was planning to pass up an event featuring the descending symbol -- in contrast to the District's Barry, who led the countdown here. Koch was scheduled to be at a midnight swearing-in ceremony that officially would kick off his third term as mayor of the Big Apple.

Too busy to celebrate New Year's Eve, Koch also was too busy to pooh-pooh Washington's claim to a New Year's rivalry, but press aide Judith Burrell did it for him, saying Koch believes "nothing can replace or take the place of New Year's Eve in New York City."

Of course, no one said putting on the glitz -- or challenging New York's traditions -- would be easy.

With Barry's promise to top New York's reputation, the city rolled up its sleeves early yesterday and got down to the nitty-gritty of making the big party work.

On the last day of 1985, streets and local offices were nearly empty while hair salons, party supply shops and liquor stores were filled with would-be revelers working out last-minute details for party plans.

Earlier yesterday, the Pavilion was abuzz with technicians, stagehands and other workers scurrying around in a controlled frenzy.

Restaurateurs girding for brigades of revelers busied themselves with ordering champagne and harder liquors by the truckload while local police hunkered down for a night that has earned an infamous reputation for drunk driving.

Many area hotels offered special New Year's Eve packages -- a party, dancing and a room -- and did a brisk business.

Barry Hoehn, spokesman for the Radisson Mark Plaza Hotel in Alexandria, said all three party packages offered by the hotel had sold out.

"We started selling the packages right after Thanksgiving, and by the time Christmas came around it was Katy bar the door. I'm surprised we sold out so fast, and we are absolutely looking forward to it."

Also participating in the city's celebration were residents of a homeless shelter at 425 Second St. NW, which is run by the Community for Creative Non-Violence. CCNV leader Mitch Snyder said the organization was planning to throw a small party of its own, with food and other provisions donated by private groups, for residents. But, he said, many of the homeless living there would go down to the big bash on Pennsylvania Avenue.

"Most of them will go by the Pavilion tonight," Snyder said. "They have a nice time there."

Preparations for the downtown celebration, handled by the Mayor's Committee to Promote Washington, were begun in the spring and entailed a wealth of details.

But the two persons who let Washington officially know that the new year had arrived were nowhere to be seen.

Throughout the day, Richard Mountjoy and James Caldwell, the men responsible for lowering the giant stamp labored in obscurity, inspecting guide wires and the timing of the elaborate rigging that would lower the 900-pound replica of the "Love" stamp.

"It's a good feeling to lower the stamp," said Caldwell. "You feel like you're a little bit more a part of the city than everyone else. The only thing is, no one gets to see us. And we're marvelous, simply marvelous."