Construction workers putting the finishing touches on the new Washington Convention Center did something unusual one fall afternoon: They took a long, lavish break together.

Hundreds of them in their red, white, blue or green hard hats -- some plastered with U.S. flag stickers, others with "Be Union" printed on the side -- put away their tools to munch on hamburgers and chili in one of the nearly finished exhibit halls. The break was a pep rally to honor the men and women bringing to life the biggest building ever erected in Washington, and it featured former Washington Redskins linebacker Ken Harvey and the team cheerleaders.

The event marked a turning point in the center's 17-year history, starting from its conception in 1986 through the October day in 1998 when 14 business, political and community leaders turned the first scoops of earth with steel shovels during its groundbreaking. Workers had been on the job since. A few of them walked away from the rally with tickets to Redskins and Ravens games.

Then came Crunch Time.

That's what convention center officials called the rally and the period leading up to the building's March 31 completion, and indeed it has been. Since the September rally, 1,400 workers have swarmed the Mount Vernon Square site six days a week -- 1,100 on the 6:30-a.m.-to-3-p.m. shift, 250 on the 3-to-11-p.m. rotation and 50 from 11 p.m. to 7 a.m. An additional 300 work Sundays. When carpenters installed 3,000 sheets of drywall -- five truckloads -- in just four days last month, it was one of many feats of man, machine and moxie typical of the final six months of construction.

"You see the finish line in sight, and everybody's in full gallop," said Gregory S. Colevas, project executive for the site's construction manager, Clark/Smoot. Colevas needed a calculator to put the frenzied pace into perspective: In recent months, he said, workers have installed about $5 million worth of stuff -- carpet, drywall, stonework and other necessities -- every week. "I've never seen a job before with 50 painters," he said.

Colevas and other project leaders said the hard work has paid off. The $834 million facility in the Shaw neighborhood of Northwest Washington is set to open on time. With the deadline a few weeks away, the building is about 95 percent complete, officials said.

The 17-acre roof is sealed, and much of the exterior skin of limestone, glass, brick and precast concrete is in place, cleaned and polished. Inside, the building's 70 meeting rooms, 700,000 square feet of exhibit space and grand ballroom lack only flourishes. The bold red, green, blue and gold patterned Axminster wool carpet from Ireland has been laid out in most areas, most of the 20,000 gallons of off-white, pale gold and pale gray paint is rolled onto walls and ceilings, and phone equipment that can handle 1,320 simultaneous calls was installed inside an operations center days ago.

Plywood still protects the granite floor of the two-block-wide central lobby while workers on scaffolds secure African makore paneling to the walls. Inspectors are still running some of the building's 69 elevators and escalators to make sure they meet city and national safety requirements. But the heating, cooling and emergency power systems are up and running, and bucket-and-sponge brigades have been cleaning up the dust.

"The moment has arrived," a proud Lewis H. Dawley III said last month at a D.C. Council hearing. As general manager and chief executive of the Washington Convention Center Authority, Dawley is maestro of a thousands-strong orchestra of convention center staff, architects, engineers, construction executives, electricians, painters, stonemasons and others. They have faced natural and manmade hurdles on their way to March 31, including rising costs, an April 2001 collapse of some steel roof trusses, recent snowstorms that slowed some outdoor work and a steady flow of complaints from businesses and residents for everything from noise to ill-mannered workers to traffic congestion.

The opening of the six-block, six-level building is sure to mark even more changes in the rhythms of commercial and residential life in Shaw but is seen by officials as the catalyst for jobs and dollars in the regional economy, attracting hundreds of thousands of convention-goers and providing a new anchor for the northern edge of downtown. "Here at Eighth and N, we have been preparing for several years now for the birth of a major baby, and this one is huge," said the Rev. James D. Watkins of the 140-year-old Immaculate Conception Church, which faces the new center.

Although other, minor events and a celebratory series of grand openings come earlier, the center opens for business April 8, when the Federal Office Systems Exhibition (FOSE), a trade show for government contractors, becomes the first convention at the site with 60,000 attendees. Grand-opening festivities begin a three-day run March 28, with dinners and receptions for prospective clients, members of Congress and city and community leaders. A ribbon-cutting gala is set for March 29, and a cake-cutting for March 30. Public events are planned through the summer.

Convention center officials are quick to say not everything will be operational March 31 -- or even for the first convention. Some fiberglass and metal-frame outdoor canopies will not be up until April or May. The 18,000-square-foot restaurant area at the building's southern end will not be completed until the end of May and perhaps later. Some of the center's 44,000 square feet of retail space will not be ready until Sept. 30, at the earliest.

But Allen Y. Lew, the authority's managing director of development, said such elements are amenities that "do not affect the way we operate the building." He said the authority wanted the food-service operator, Centerplate, to craft a unique restaurant space for itself. "It has to be their stamp," Lew said.

Washington's 20-year-old convention facility at 10th and H streets NW closes April 1 -- one day after the March 31 completion. The new convention palace is three times as large. The last event scheduled at the old center is practice for the 2003 World Figure Skating Championships. The future of the 10-acre site remains undetermined, but the fate of the building is not: Convention center officials plan to demolish it.

City, convention and tourism officials expect the new center to be a much stronger economic engine for Washington and the region. They anticipate the new Washington Convention Center pumping $1.4 billion into the economy, creating 17,000 tourism-related jobs and drawing 3 million visitors a year. Tourism leaders said the site opens an untapped market in the Washington tourism trade, conventions and exhibitions that ignored the city because the old center was outdated and too small.

Already, almost 200 meetings and conventions are booked into the new building through 2013. The building is big enough to accommodate two medium-size events simultaneously, as in June, when 4,000 attendees of the American Physical Therapy Association's annual conference are to share the space with the 17,000 attending the Biotechnology Industry Organization's annual meeting.

Project designers say the convention center is the sixth-largest in America. The stately ballroom's 52,000 square feet make it the biggest of its kind in Washington and one of the largest on the East Coast; the spacious main lobby is equal in size to the nave of Washington National Cathedral; and the entire building, at 2.3 million square feet, could accommodate two Washington Monuments lying end to end. The building is wired to draw enough power to support a town of 7,500.

Just fitting such a mammoth facility into a six-block area posed a challenge. It stretches south to north from Mount Vernon Place NW to N Street NW, east to west from Seventh Street NW to Ninth Street NW.

Architects from three firms -- Mariani Architects Engineers and Devrouax & Purnell, both of Washington, and Thompson, Ventulett, Stainback & Associates, of Atlanta -- solved the puzzle by placing only a third of the building above ground and breaking that third in the middle with two bridges so pedestrian and vehicle traffic could cut through, rather than have to detour around, the massive center. They crafted something of an architectural chameleon, a building that displays a grand glassy face to downtown at its southern end and another, more subdued, brick-based look to fit into historic Shaw in the north.

"It had to be friendly with the neighbors," said Theodore F. Mariani, the founder of Mariani Architects Engineers. "It couldn't overwhelm the community."

Inside are amenities and gizmos galore. There are the sculptures and paintings that will eventually be part of a $4 million public art program and the 42,000 square feet of African paneling in the lobby and ballroom that cost $50 per square foot. The authority even plans to buy two Segway Human Transporters -- the futuristic, two-wheeled scooters -- to make it easier for staff members to get from one place to another in the vast guts of the place.

Security, after Sept. 11, 2001, has gotten a lot of attention. "The new building has the latest in high-tech security measures," said convention center spokesman Tony Robinson, listing such measures as motion detectors and surveillance cameras.

The center's opening marks the culmination of years of work for many of those involved. It was in May 1997 that Colevas first looked at drawings of the convention center project. He was 35 then. He's 41 now. "To walk the job now and to see this magnificent facility, it gives me a nostalgic feeling," he said.

Work has already changed things in the immediate area. Last month, city transportation officials shut Mount Vernon Place between Seventh and Ninth streets, including the intersections at New York and Massachusetts avenues, to speed roadwork construction.

The resulting tangle of Jersey barriers, detours and traffic has frustrated motorists and business owners. Several businesses, many that make up the Mount Vernon Business Alliance, have complained that construction combined with roadwork has driven away customers, turned their storefronts into outposts and made running a hair salon, furniture store or theater a daily struggle. "The convention center has tried to mitigate the problems that we faced," said Paul W. Ruppert, 35, executive producer of Warehouse Theater, which faces the new center on Seventh Street. "The problem is that the problems with construction are just so severe."

Ruppert said the construction and roadwork-related traffic has led to a small decrease in theater attendance and postponed the opening of a year-round cafe. Last Friday, a lead actor in "Cervantes: The Interludes" got stuck in traffic, and the 8 p.m. show was canceled.

Convention center officials say they've done their best to be good neighbors. The authority has spent nearly $1 million on surrounding small businesses, including supplying roughly $370,000 in grants and claims for business losses and negative impacts. Officials also have provided free shuttle service at one of three lots they leased for parking for the merchants, customers and residents.

Convention center officials meet each week with the business alliance and have promised additional compensation for roadwork-related losses. The intersection at Seventh Street should reopen next week and Mount Vernon Place could reopen by the end of this month, officials said.

Watkins, at Immaculate Conception Church, said he looks beyond the daily inconveniences -- dirt has damaged the church's 19th-century organ, and his chores now include sweeping up outside almost every day -- and sees a bigger, rosier picture for the neighborhood come April. "Change is never easy for anyone," he said, "but change brings about opportunities for growth and life."

The main entrance is two blocks wide, its floors granite and its walls being covered in expensive African wood.Six days a week, as opening day approaches, about 1,400 workers turn out to clean and apply the finishing touches.