Laotians have a musical instrument called the khaen, a mouth organ of bamboo pipes that traditionally accompanies social occasions, providing a backdrop to revelry.

It produces music with a lilt, the kind that gets listeners dancing an impromptu jig. And toes were indeed tapping Saturday at Wat Lao Buddhavong, a Buddhist temple near Catlett in Fauquier County, where about 600 people had gathered to soak up the merriment.

The occasion was the Boun Bang Fai, or rocket festival, an annual event in Laos intended as a plea to the god of rain to help deliver a bountiful harvest. Rockets, built from bamboo and colorfully decorated, are launched as a gesture to the god.

Gunpowder fuels the rockets, but the party fuels the rocket festival. So when the Smithsonian Institution approached members of Wat Lao Buddhavong and asked for such a rocket to display in an upcoming exhibit at the National Air and Space Museum's Steven F. Udvar-Hazy Center, the temple decided to send it off with a Boun Bang Fai -- apparently the first in the Washington area in nearly 20 years.

"This is something we're very proud of," said Souk Sayasithsena, a member of the wat's board of trustees who lives in Annandale. "We wanted to deliver it in the way that the festival was conducted at home, which includes all the dancing and singing."

And the khaen. And drums and tambourines. And firecrackers hissing and screaming behind dancers. And vendors in tents selling fried sweet potatoes, coconut cakes and noodles. Chicken and meatball skewers sizzling on the grill.

All this, centered around a rocket.

Frank H. Winter, curator of rocketry for the Smithsonian, attended his first Boun Bang Fai on a trip to Southeast Asia in 1977. The bamboo rocket captivated him.

"The biggest mystery to me is how these people know about making rockets when they're basically farm people," he said. "There are no classes they take or textbooks to look at. They just know how to make these things as part of growing up. It's just tradition."

The rocket donated to the Smithsonian is smaller than traditional ones, about 14 feet long instead of 50 to 60 feet. It is made entirely of bamboo, honey brown and unfettered by the brightly colored paper that coats many Laotian rockets. Along its spine sits a naja, the god of snakes, a detailed sculpture -- each scale delicately carved -- created by Praphonh Phongsavan.

Phongsavan, who works for Washington Gas, labored over the naja on nights and weekends. He even spent his one week of vacation working on it.

"It took a long time to do that whole thing. It's hard work," he said.

Phongsavan's effort is typical of the care that goes into making the rockets in Laos, Sayasithsena said. The rockets are judged on two qualities: beauty and distance. None of the four rockets at Saturday's festival was launched because of fire regulations.

In Laos, tradition holds that if a rocket doesn't become airborne after it's fired, the builder of that rocket is thrown into the mud.

"It becomes very dirty," Sayasithsena said. "Dirty in the sense of getting soiled, but also, during the dancing, they display sexually oriented materials just to have fun. And it's a sign of fertility."

This is the part many Laotians remember about a Boun Bang Fai: men painting their faces, wearing women's clothing and singing bawdy songs. Saturday's event, where only the female dancers wore the elegant, colorful dresses, was comparatively tame. This was partly because of the absence of alcohol. (The Fauquier temple does not encourage drinking.) At a typical rocket festival in Laos, a procession carries the rocket through the village, people stopping at houses along the way for drinks of alcohol.

"Just like Halloween, the houses by the roadside would tend to prepare themselves for that," Sayasithsena said. "When they don't have anything to offer, it doesn't look good."

The timing of the festival also deviated from tradition. The festival typically is held in May, just before the planting season, giving farmers a chance to cut loose before beginning months of intense labor. June also marks the start of the Buddhist Lent, a three-month period of sacrifice, such as giving up drinking or smoking.

"We are so busy planting rice, and the Buddhist Lent is coming, you just want to have fun beforehand," said Sutat Saoman, a Germantown resident who was born in northeast Thailand, where Boun Bang Fai is also celebrated. "You go have a good time before you do something holy."

Not that anyone seemed disappointed by the more conservative atmosphere Saturday. Most in the crowd were happily moved by the music, the dancing, the food -- and the deluge of memories. Save for those who have returned to Laos to visit family and friends, most transplants haven't seen a Boun Bang Fai since they left their homeland.

There's talk already about making the festival an annual event at Wat Lao Buddhavong -- with one notable change.

"The next time it happens," Sayasithsena said, "it will probably be in May, at the right time."

The rocket given to the Smithsonian rests in front of monks of Wat Lao Buddhavong temple during the donation ceremony Saturday. Frank H. Winter, right, the Smithsonian's rocketry curator, speaks at the ceremony during which a traditional Laotian rocket was donated to the Steven F. Udvar-Hazy Center.