The celebration of the Vietnamese new year, Tet, has changed for Hoang My Hien since her move to the United States.

"I felt very sad during my first Tet in America six years ago," recalled Hien. She said she and her family and several friends spent that first American Tet together in low spirits, worried about their future and finding jobs, and lonely for the home they had left behind.

This year, their mood is better. The Vietnamese residents, who began arriving here in large numbers six years ago depressed and bewildered after the fall of the South Vietnamese government, are more optimistic about their lives now.

Hien, her family and friends will gather again this year and, in a custom picked up from their American neighbors, the event will be potluck.

For the nearly 15,000 Vietnamese living in the Washington area, Tet, which begins Monday, marks everyone's birthday as well as the new year, according to the lunar calendar. The most important holiday for the Vietnamese, it is a time of celebration and the welcoming of spring, as well as the season for families to visit and care for the ancestral graves. Of deeper significance, Tet is dominated by the firmly rooted concepts of fortune and propitiation of the gods and the ancestors.

Because of its spiritual significance, Tet is the time when Vietnamese refugees here most long for home, and when many pay special attention to traditions and rituals. For weeks in advance, many prepare special holiday foods, such as the traditional cake made of sticky rice, with pork, eggs and green bean paste inside, and a variety of preserved or pickled foods.

Seven days before Tet, a food offering is made to the kitchen god, who will make his annual report to the Jade Emperor of the universe, according to legend.Custom calls for the entire extended family to congregate at the family altar on the first day of Tet to thank their forebears for their existence and request the traditional blessings of happiness, prosperity and longevity.

Superstitions connected with the holiday abound. Many seem to have sprung from a need to live in harmony with one's family, friends and environment. Before Tet, debts must be paid off, mistakes forgotten, offenses pardoned and faults corrected. Hospitality and friendship must dominate the three-day celebrations, and conflict and anger must be avoided.

Because happenings on the first day of Tet are thought to affect the coming year, many Vietnamese observe traditional taboos. No one must visit another's home on the first day of Tet, unless asked, because that initial visitor is thought to determine the luck -- or misfortune -- for the host family during the entire year.

Some Vietnamese said last week, only half jokingly, that they want to take off work on the first day of Tet so that they will not be burdened by hard work for the rest of the year. But a Springfield Xerox technician quipped, "I want to go to work on that day in order to have work around the year and not get laid off."

Tet has a festive side, too. Homes, shops and businesses are decorated with flowering apricot, peach or cherry branches, flowering narcissus plants and yellow chrysanthemums. Fireworks, parades and traditional dances are held.

Each person wears new clothes, and good wishes are exchanged. Gifts of new money carefully folded in specially made small red envelopes are believed to bring good luck during the year.

Although most customs are maintained by Vietnamese residents here, the ways of celebrating have changed somewhat.

Hien, a social worker in Arlington, said most Vietnamese celebrate more simply than they did in Vietnam, with fewer visits to friends and relatives, fewer vists to pagodas on the eve of Tet and fewer days off from work.

"I have sent greeting cards for Tet to friends and relatives," she said. "My family will recite prayers in front of the ancestors' altar before dinner. I will not make rice cake but I will have some Vietnamese marmalades."

Hien, dressed in a hand-embroidered, purple ao dai, a traditional Vietnamese dress, said she would take two days off work to honor Tet, instead of the customary three days.

At Pulsecom, a telecommunications company in Falls Church, 20 Vietnamese employes petitioned their employer for time off to observe Tet. The firm agreed.

Nguyen Trung Giang, the father of five children, two of them born in the United States, said, "I usually take vacations twice a year, one in summer with the children and one at Tet." He allows his children to stay home from school on the holiday, but added, "I don't force them."

Conditioned by years in the United States, the younger Vietnamese children do not know as much about Tet as about Christmas, said Giang, a computer technician employed by Hughes Aircraft Co. in Arlington. "But they like Tet since on that day I keep the practice of li xi (giving money) in small red envelopes," he added, grinning and pointing to his wallet pocket.

Perhaps a sign of optimism among the Vietnamese refugee population here is the number of public events organized this year to celebrate Tet.

The Council of Vietnamese Associations planned an arts festival, a Vietnamese movie showing, a poetry contest, a special broadcast, a fair and a reception. A shipment of magazines and money has been sent to refugees still in Southeast Asian camps. The Vietnamese Navy Veterans Association, the Vietnamese Lawyers Association and other groups have held parties and dances.

In addition, an invitation-only reception is planned next week as the Vietnamese community's thanks to persons and governments who have aided refugees. Guests will include prominent U.S. government and congressional leaders, representatives of nations that have provided first-country asylum or have resettled refugees, and guests from private organizations that have helped Vietnamese.

New Year events will include:

Tet Fair. Saturday, 10 a.m. to 5 p.m. at Kenmore Intermediate School, 200 S. Carlin Spring Rd., Arlington.

Vietnamese Folk Opera. Saturday, 7 p.m. at Fairfax High School, 3500 Old Lee Hwy., Fairfax.

Tet Fair and Cultural Performance. Saturday. Fair from 10 a.m. to 3 p.m., cultural performance at 3 p.m. at Montgomery Blair High School, 501 Dale Dr., Silver Spring, Md.

Traditional Service in Honor of the Ancestors. Saturday, Jan. 30, 11 a.m. at Kenmore Intermediate School, 200 S. Carlin Spring Rd., Arlington.

Special radio broadcasts Sunday will include:

WHFS (FM 102.3), in Vietnamese, 9-10 p.m.

WETA (FM 90.9), in English. This broadcast is to introduce the Tet customs to the local American community, followed by an interview with four Vietnamese community leaders. 11:30 p.m. to midnight.

WETA (FM 90.9), in Vietnamese. Special New Year's Eve broadcast. Midnight to 1 a.m.