A vast and well-behaved throng of 100,000 high-spirited, hand-waving, horn-honking revelers burst into cheers last night as the descent of the new Love Stamp from the Old Post Office tower ended the old year and ushered in 1988.

A hoarse-voiced Mayor Marion Barry led the countdown of the seconds as the giant, illuminated image of the stamp, depicting a pink rose, glided down the 13-story tower, consigning 1987 to history, in a ceremony that has become a Washington tradition.

Earlier, as 1987 entered its last hours, many members of the crowd, who gathered in the closed-off sections of Pennsylvania Avenue between 10th and 14th streets NW arrived searching for a good time.

One hour before midnight, Durwood (Jazzy) Basnight danced and sang on the corner of Pennsylvania Avenue and 12th Street NW, explaining why he felt compelled to celebrate in the street. "When you're a people person like me, and you know there's a happening like this, you got to come. What else can you do?" asked the 33-year-old Northeast Washington resident. "I'm mingling, drinking, having fun, meeting, greeting, and talking it up, especially to all the ladies, women and females around."

Police on motorcycles threaded their way through the crowd in the open space near the District Building and the National Theatre, while blue spotlights swept across the facades of the buildings, enhancing the festive atmosphere provided by the strings of lights bedecking trees.

Steve Witzen, 30, and Pam Goodrich, 24, both of Alexandria, explained their presence downtown in a similar way: She "wanted to feel the excitement," Goodrich told a reporter. "You have to come here to feel the spirit."

"I'm hoping for a lot of good things in 1988," she said.

The Pennsylvania Avenue revels were not the only party in town, of course. Two groups greeting the New Year last night were separated in distance only by the width of Farragut Square but were in many ways worlds apart.

Men in tuxedos and woman in gleaming gowns danced in the Army-Navy Club on one side of the square. Little more than 50 yards away, about a dozen men wryly congratulated themselves and interested passers-by on the advent of 1988 while bundled in a bus outside the Farragut West Metro station that is being used as a shelter for the homeless.

At Walter Reed Army Hospital the crowning event of the evening was the birth of Courtney Lemaitre to Army Cpl. Sheila Lemaitre. The 6 pound 11 ounce, boy was delivered by Capt. Deborah LaBeau at 45 seconds past midnight.

For most revelers, though, the highlight was the timed descent of the Love stamp. Cindy Kline, 25, and Pamela Young, 26, both of Manassas, took seats at 7:30 p.m. on a bench in front of the tower to be certain they had a good vantage point.

"We knew it was going to be crowded," Kline said, "and we wanted to get here early so we would have the best seats to see this at midnight."

Witnessing the descent of the stamp from close range, she said, shivering in the evening's chill, was "something that we always wanted to do, but this year we got brave enough to actually come out here."

After more than two hours of waiting, Young consoled herself and her friend by observing: "Well, we're halfway there now. It shouldn't be too hard to make it till midnight."

About two hours before midnight, the crowd, which traditionally has been slow to reach its peak size, appeared to be well into the thousands, and represented a wide range in age as well as areas of the metropolitan area.

But despite the diversity in age and background, almost all of those queried last night were united in expecting better things from the New Year. Only their reasoning differed.

Cindy Kline said she believed 1988 would be better "because it's an even number." Its predecessor "was an odd number," she added, "and it was an odd year."

Behind the gray stone walls of the pavilion was an admission-by-ticket-only world of sequined glitter and tuxedoed elegance, but it was strikingly similar to the celebration outside in its enthusiastic optimism about the coming year.

Since the event began in 1983, the District has engaged in something of a competition with New York for the rights to claim the nation's most renowned celebration of New Year's Eve.

Two years ago, rowdiness and a homicide tarnished the glamor and ebullience of Washington's festivities, but last year, the crowd was described as well-mannered.

Police said they made five arrests. One man was charged with indecent exposure after he allegedly exposed himself to two women. The other arrests were minor.

"It was much more orderly than I would have expected," said Cliff Esser of Annandale, who attended the celebration with his wife, Cam. "The weather was favorable, and I never saw anyone falling over drunk."

Like others on the street, the Essers offered bittersweet reflections on the past year, and expressed fears about the economy. "I think the stock market scare made a lot of people stop and think," Cliff Esser said.

But as 1987 flickered away, and downtown crowds gathered, several participants at last night's bash appeared to reflect the sentiments of Cecilia Grillo of the District, who said, "This seems to be getting bigger and better every year."

Staff writers Martin Weil and Peter Pae, and editorial researcher Cathy Wall contributed to this report.