Five blocks of Constitution Avenue NW will be closed starting Tuesday evening as the District begins final party preparations for thousands of guests it expects New Year's Eve at its "Main Street Millennium" celebration.

And as the calendar counts down next week to 2000, at least one more street a day will be shut so that workers can build stages, erect pavilions, run power lines and set up exhibits. Given that and the Dec. 31 festivities on the Mall, which will make long stretches of downtown streets off limits for parking, city officials yesterday pushed a singular message:

Come on down to the party, but take Metro, take Metro, take Metro.

At a balloon-festooned and blues-serenaded news conference, officials alternated between the fun aspects of their free two-day street party and the nitty-gritty details that will make it fly or flop. Their Metro mantra emphasized significant concerns about traffic, parking and security.

Constitution Avenue, they said, will be closed at 8 p.m. Tuesday between 9th and 14th streets and remain closed through 11 p.m. Jan. 2. The next night, 12th Street between Independence and Pennsylvania Avenues will be shut.

The D.C. police department, in response to State Department alerts about potential terrorism abroad and at home over the New Year's weekend, will stage a "historic deployment," with more than 400 officers on duty at the city event alone.

"While there is always a risk because of where we are in this country, and where we are as the nation's capital . . . we're ready for whatever happens," Mayor Anthony A. Williams (D) declared.

Beer, wine and champagne will be sold at the celebration--it is New Year's Eve, after all, one organizer pointed out. But alcohol consumption will be monitored by IDs and wristbands, and all bubbly must be consumed within the boundaries of 10th and 14th streets.

There will be one prominent lost-children tent, six medical-care zones and eight booths where partygoers can buy tickets for the food and drink that will be served at four heated pavilions throughout the festival area. Tickets, including a 20 percent surcharge commonly assessed at the Taste of D.C. Festival, will sell eight for $5. Items will require differing numbers of tickets.

Officials said yesterday they have raised about $430,000 of their $750,000 budget and expect souvenir and food sales to cover the rest, in large part through the ticket surcharge. Any profits will go toward activities next year to mark Washington's bicentennial as the nation's capital, including a nonprofit parks conservancy that the city hopes to debut early in 2000.

"We're trying to make sure that every kid in the city has a chance at a childhood," said Sandy McCall, executive director of Millennium Washington, the city's New Year's and bicentennial commemoration.

The conservancy is in the planning stages, but McCall hopes to model it on the program that restored Central Park in New York City. It would be run by a still-unnamed steering committee and work closely with the city Parks and Recreation Department. Through tax-deductible contributions from individuals and corporations, McCall explained, the conservancy could help fund everything from tree plantings to youth programs to equipment purchases.

"Two years from now, any kid who wants to play Saturday basketball . . . will get the chance," he pledged.

City and federal officials aren't sure how many people to expect for the city's celebration, the daytime programs the Smithsonian Institution is offering at three museums through Jan. 2, or the glitzy New Year's Eve show at the Lincoln Memorial that will feature fireworks and a bevy of celebrity entertainers bundled up against the late-night chill.

"We have never had a big millennium event before, obviously," McCall laughed.

Climate will likely play a big role in determining the turnout. The National Weather Service won't issue a forecast until five days ahead; the average temperature for New Year's Eve in Washington is a high of 43 degrees and a low of 28. But "warm or cold, snow or not," the mayor stressed, the party is on.

For those braving the weather at the Lincoln Memorial, Metro said yesterday that it will run free, homebound Metrobus shuttles from a stop at Independence Avenue and Ohio Drive to its Rosslyn, Waterfront-SEU and Pentagon stations, and from Constitution and 20th Street to the Farragut North and Farragut West stations.

The city celebration kicks off at 11 a.m. Dec. 31 at 12th Street and Constitution Avenue, where President Clinton, Hillary Rodham Clinton and Williams will unveil a special time capsule. Entertainment will continue until midnight, and resume Jan. 1 from 11 a.m. to 6 p.m.

Four pavilions--one for each quadrant of the city--will showcase exhibits and musical performances, and historical reenactors, jugglers and acrobats will wander throughout. Partygoers will be able to send e-mails and digital postcards at a technology pavilion or have their picture taken for a "photo quilt" that will be part of a multi-image time capsule.

CAPTION: At a news conference for the city's Millennium fest, the Anacostia High School marching band performs in front of Lincoln Theatre on U Street.

CAPTION: Mayor Anthony A. Williams talks with Sandy McCall, executive director of the city's Millenium Washington celebration, outside Lincoln Theatre.

CAPTION: Blues singer Mary Jefferson, 70, who started singing on U Street when she was 14, is to perform at the celebration.