From the steps of the Lincoln Memorial to the aisles of a Burtonsville grocery store and the emergency operations headquarters in Fairfax County, dress rehearsals for both celebration and disaster filled the final hours of preparation yesterday for the most anticipated New Year's Eve of this or any millennium.

Government agencies and private companies alike tested computer programs yet again to make sure their systems recognize the new calendar's double-nought as 2000--averting, they hope, any Y2K crashes that could wreak havoc on power, telephones and other aspects of modern life.

Shoppers stocked up, nonetheless, just to be safe. Some local grocery stores and gas stations reported higher than usual business but assured customers that their inventories are not depleted.

Performers from Don McLean to Kathy Mattea rehearsed their numbers on the massive outdoor stage that the Lincoln Memorial has become, a scene of organized chaos of musicians, set-builders, cables, cameras and squealing microphones that tonight will jell into a kaleidoscopic extravaganza of sound and light.

"Ladies and gentlemen, your host for America's Millennium, Will Smith!" the announcer practiced repeatedly yesterday, despite the actor-singer's afternoon absence.

And police forces, already on heightened alert because of security concerns, reviewed their preparations for the tens of thousands of people expected on the Mall and the major crowds likely to be lured to numerous other public celebrations across the Washington region. District officials even have a new mobile command center, equipped with infrared camera, generators and satellite phones, capable of responding to such catastrophes as riots or terrorist attacks.

"We are definitely taking a lot of precautions," said Sgt. Rob MacLean of the U.S. Park Police, which will deploy hundreds of officers for the Lincoln Memorial extravaganza. State Department alerts in recent weeks have warned about possible terrorist threats both abroad and at home, but MacLean stressed, "We do not have any specific threats for this event or any monument."

An equal show of D.C. police force will be evident at the city's two-day block party along Constitution Avenue NW, and some of those officers were kept busy yesterday responding to three separate bomb alarms. All were false.

The first occurred about 6:40 a.m. when bomb-sniffing dogs doing a routine check of the Ronald Reagan Building and International Trade Center signaled the possible presence of explosive chemicals. At 3:30 p.m., police searched the Adams National Bank branch at Union Station because of a letter saying a bomb had been placed there. Half an hour later, a report of a suspicious package at Chevy Chase Pavilion forced evacuation of that shopping center and the nearby Mazza Gallerie, as well as closing several blocks of Wisconsin Avenue during rush hour.

"These fake threats are something that we, unfortunately, know we are going to have to spend a lot of time looking into over the next few days," said Officer Kenny Bryson, a police spokesman. "We don't want to alarm people, but we have to look into each one."

For the most part, though, the penultimate countdown focused on the future.

"Everything we have done is ready," said Quentin Banks, spokesman for the Maryland Emergency Management Agency. "We are just waiting for the time to come upon us."

At the state's emergency operations center in Reistertown, representatives from more than 30 federal, state and nonprofit agencies drilled once more with software designed to track any possible problem. Still, the day was one of relative leisure. Even Y2K information hot lines were quieter than usual.

Some restless county leaders hit the streets, however. Howard County Executive James N. Robey (D), a former police chief, toured public buildings and emergency centers in a spot inspection of county preparedness. Montgomery County officials deployed portable stop signs in case of power malfunctions.

At the Burtonsville Giant, Noble and Denise Jolley lay in supplies. "I think there are only going to be sporadic problems, but you never know," she said, glancing at the five gallons of water and 24 rolls of toilet paper in their cart. "With five teens in my house, you can't take a lot of chances."

Those worries aside, this is a New Year's Eve fraught with complications--the most contentious of which is the mathematical reality that, zeroes or not, 2000 is one year shy of a new millennium.

But few have paid attention to that distinction, and hotels and special events have promoted it to the hilt, with prices to match. Since Thanksgiving, numerous celebrations have been scaled back or scrapped, including, this week, a huge affair at MCI Center and a turn-of-the-century masquerade ball that was to have been part of the Maryland city of Frederick's ringing-in. According to a USA Today/CNN/Gallup Poll released yesterday, nearly three-fourths of Americans still had no special plans for tonight.

With some, blame procrastination. In the Washington area, numerous businesses that specialize in catering, limousines and babysitters found themselves besieged this week for last-minute assistance.

At White House Nannies Inc. of Bethesda, the calls in the last few days became increasingly urgent, according to Mary K. Lyddane, director of temporary services.

"It's been pretty busy," Lyddane said between efforts to aid several hotels in locating sitters for their guests. "We've been able to place some sitters, but we're still working on getting help for other families."

One nanny was able to negotiate a lucrative deal with a couple who plan to celebrate the New Year by staying out all night. For a flat fee of $600, she will arrive at their home this afternoon to feed her charges dinner. She then will spend the night, get up with the children and feed them breakfast.

Other families have planned a celebration to include young and old alike. Edwin Jesiolowski, a Haddonfield, N.J., architect, should be arriving in Washington this afternoon with 19 relatives and friends, including eight children, all pumped about the fantastical fireworks finale promised on the Mall at midnight.

"My wife is a fireworks nut," he said earlier this week, explaining why he had called Fireworks by Grucci, the Long Island pyrotechnics company doing the show, to determine the premier place to be Dec. 31.

"They said, 'If you want the best of the best that we've ever done, go to Washington.' " So, he recounted, "I told my wife, 'We're going to Washington.' "

Some of what Jesiolowski and crew will get, well before the clock strikes 12, was on display yesterday afternoon, to the delight of an impromptu audience of hundreds who strained to see celebrity performers during an extended rehearsal.

Capt. Tom Walczyk, a dentist with the Navy, strolled over from his nearby office--and will return tonight.

"This is the essence of America," he said. "To be able to touch and see this. . . . It's got all the lights, the actors, the music, the volume. It epitomizes gung-ho America."

Jennifer Schonberger, 16, a junior at West Springfield High, felt a little disappointed that she couldn't get closer to the stars on stage. But just approaching ground zero of millennial hubbub made the trip worthwhile for her and her mother, Farideh.

Not that the Schonbergers will be grooving on the Mall tonight. They have a party scheduled with friends.

Program organizers say they are expecting 100,000 revelers, though since this New Year's gala is a first, they have no real way of estimating the turnout. Four large screens are in place on the west and south sides of the Reflecting Pool, which is how the real-people crowd will see most of the action. A sizable contingent of VIPs, including the president and first family, will enjoy up-close seats and bleachers.

The public must enter the area through four gates on Constitution Avenue, Independence Avenue and 17th Street, and anyone is subject to a search by Park Police. Security measures will force closure of the Last Firebase, a camouflage-painted kiosk near the foot of the Lincoln Memorial where veterans sell souvenirs and keep hope alive for comrades missing in action. Their vigil has continued nonstop since 1986, but tonight, per U.S. Secret Service orders, they'll shut from 9 p.m. until the president departs.

As yesterday's dry run of the nearly $13 million spectacle proved, the croonings of Tom Jones, Kathleen Battle's soaring high C's, the clashing chords of "Also Sprach Zarathustra" and the percussive parade of the Broadway show "Stomp" will carry nearly to the Washington Monument.

"This is the place to be if you're going to be anywhere," Jones told reporters. Asked if this was how he had envisioned the century's end, the 59-year-old veteran entertainer cracked, "It's good just to be here, to still be alive at this point."

Minutes later, Kris Kristofferson laughed off the notion that anyone should be worried about security during the evening. "I have concerns about breathing," said the singer-songwriter, 63. "I'm an old man. I have concerns about being hit by a car. I don't live in fear of terrorists."

Staff writers Rajiv Chandrasekaran, Stephen C. Fehr, Raja Mishra, Tracey Reeves, Michael D. Shear, Emily Wax and Scott Wilson contributed to this report.

New Year's Performances

The "America's Millennium Gala" at the Lincoln Memorial tonight features nearly 500 singers, musicians and dancers. The tentative lineup and schedule of the three-hour show includes:

9:58 p.m. National Anthem, Bobby McFerrin.

10:01 p.m. Opening, Will Smith.

10:18 p.m. Tom Jones, Kenny Rogers, Foreigner, Don McLean.

10:23 p.m. Welcome, Hillary Rodham Clinton.

10:27 p.m. Trisha Yearwood and Brian McKnight.

10:33 p.m. Avery Brooks.

10:40 p.m. Kathy Mattea, Luther Vandross, Mark O'Connor, Kris Kristofferson, Usher, BeBe Winans, Patti Austin.

10:45 p.m. Jack Nicholson, John Fogerty, Vernon Reid, Slash, Nathan East, Greg Phillinganes, Kenny Aronoff, Edgar Winter.

11:01 p.m. Kathleen Battle, Jessye Norman, the Symphonic Choir, Bobby McFerrin.

11:12 p.m. Mary Tyler Moore, Brian Stokes Mitchell, the Savion Glover Tappers, Michel Bell, Renee Fleming, Tom Wopat, Bebe Neuwirth, Priscilla Lopez, cast and dancers from "Chicago."

11:31 p.m. "The Unfinished Journey" by Steven Spielberg, music by John Williams, readings by Ruby Dee, Ossie Davis, Sam Waterston, Nathan and Evelyn Hoffman, Rita Dove, Robert Pinsky, Edward James Olmos.

11:59 p.m. "Millennium Address" by President Clinton.

Midnight Fireworks and music.

12:02 a.m. U.S. Army Herald Trumpets, Symphonic Choir, World Children's Choir, Brian McKnight, Luther Vandross, Trisha Yearwood, Kathleen Battle, Renee Fleming, Jessye Norman, the Garrett Gospel Choir.

12:16 a.m. Bono and Daniel Lanois.

12:35 a.m. Broadway cast of `Stomp."

12:52 a.m. Fireworks finale and song medley.