After so many years of trying to visualize what it could be, so many years of monitoring its plodding progress and watching more than a few lavish pipe dreams go up in smoke, the people of Bangor finally got to witness a transformation of their waterfront last weekend.

For the three days of the National Folk Festival, the once-neglected strip of riverside property exploded with a vibrancy that locals only could have dreamed of years before. It was a magical moment, elevating both spirits and pride as the community proved it really was capable of pulling off an event of such grand scale.

Audrey Ambrosino experienced the same kind of magic when the National Folk Festival arrived in her hometown of Lowell, Mass., in 1987, spawning a more localized version of the event that now draws as many as 250,000 people each summer.

When the Bangor festival has completed its three-year-run in 2004, she said, the people here will ask what the people of Lowell asked themselves in 1989: OK, so what do we do for an encore?

“The Lowell Folk Festival proved that if you keep the momentum going, anything is possible,” said Ambrosino on Sunday, shouting to be heard over the zydeco music that had thousands of people dancing in the field.

Lowell, a city of about 95,000, had held a few summertime ethnic festivals over the years before the National Folk Festival came to town. But they were modest affairs, she said, that eventually ran their course. After working with the National Council for the Traditional Arts to stage its first big national folk festival, the people of Lowell were left to wonder whether it could possibly come together as they hoped.

“It was like throwing a big party without being sure if anyone would come,” recalled Ambrosino, who was part of Lowell’s original organizing effort and has continued as its publicity director. “We were expecting maybe 50,000 people, so we were blown away by the estimated 75,000 to 80,000 who showed up. It was as much a surprise to us as it is now for Bangor. You can read and hear about this festival, but until it happens you can’t imagine what it’s like.”

The festival also helped change the typical outsider’s view of Lowell as a down-at-the-heels former textile town that tourists had no reason to visit.

“The local people had heard all the negative things about their city, the bad reputation it had,” Ambrosino said. “But when you bring that many people to your town, where they’re surrounded by culture and music and fun, they leave with a completely different view. They become your ambassadors.”

When their final national festival wrapped up in 1989, Lowell residents were determined to keep the spirit alive the next year with a similar folk festival of their own.

“It’s a big civic-pride thing for a host city,” she said. “After three years, you learn what it takes to put the event on and how to make it work. You feel like you own it. That will happen in Bangor, too, if it hasn’t already. That’s part of the genius of the festival; you want it to go on and to grow.”

Because of its relationship with the Lowell National Historical Park, the National Council for the Traditional Arts has continued its involvement with the city’s festival over the years.

“We were fortunate in that regard,” Ambrosino said. “But the first year of the Lowell Folk Festival, we all were curious whether it would still have the same magic. It did.”

The Lowell Folk Festival, which is held in the heart of the city’s downtown, has become a model of how the National Folk Festival’s influence can help lift a city’s spirits and rejuvenate itself. Although the city never has officially studied the festival’s economic impact, she said, downtown merchants regard it as their biggest weekend of the year.

Should Bangor attempt its own festival after the national event folds its tents in 2004, as East Lansing, Mich., has this summer, Ambrosino recommended that it never scale back the rich diversity of musical and cultural offerings that so consistently satisfied the crowds over the weekend.

“The key is to keep up that level of excellence in the performances, and to stick with the mission of providing a festival with truly national appeal,” she said. “The people in Lowell had never heard of zydeco music before 1987, and now they’d complain if we didn’t have it.”

Bangor people have every reason to believe that a festival can be part of the life of the city and the region for years to come, said Ambrosino, who has followed the national event from Lowell to Johnstown, Pa., Chattanooga, Tenn., Dayton, Ohio, and last year to East Lansing.

“Bangor is the smallest host city in years, and had the biggest opening night anyone can remember,” she said. “From what I’ve seen, this community should be extremely proud and pleased with how everything turned out.”