The old women came dressed in traditional silk ao dai tunics, their silver hair braided beneath black velvet hair bands. Their children and grandchildren dressed in Levis and the latest American fashions, sang what they could remember of the South Vietnamese national anthem. Together they mournfully pledged allegiance to the flag of the country that no longer exists.

Among the Vietnamese and Americans gathered a few miles away at a Washington theater, however, there was no mourning. They had come together at least in part, to celebrate what one called the "victory in Vietnam."

"For me, this is a happy day," said Bui Trung, a student at the University of the District of Columbia who has been in this country since 1974. "Vietnam is free from foreign domination and has a chance to reunite."

Both groups had come together to commemorate the day three years ago when the troops of the communist Provisional Revolutionary Government of South Vietnam proclaimed the "total liberation" of Saigon and renamed it Ho Chi Minh City.

In the eyes of the world, that was the day the war ended, but it was clear among both groups assembled yesterday to mark that anniversary, that the powerful conflicts generated by the war have not gone away.

Members of the Vietnamese refugee community here have held ceremonies to commmeorate the fall of Saigon each year since 1975 when most of them came to this country as refugees. But this year was somewhat different. It was the first year the commemoration was held in the community center for the Vietnamese. The center opened last December at the old Page Elementary School in Arlington.

This year, more than the others, according to spokesman Nguyen Njoc Bich, many of the former refugees could look with pride at their lives and the advancements they have made in the past three years.

"The first year was rather sad . . . many people even cried," Bich said of the 1976 commemoration, held in Lafayette Park. "This year is more upbeat if you talk about atmosphere. The (Vietnamese) people have become quite familiar with this country now.They are better off economically."

In many cases, their English classes have been completed, and many of the men are employed and their families are self-supporting. The thoughts of the Vietnamese community, said Bich, have turned to helping those who just recently escaped from the country's communist regime.

"The main thing is to get the American government and the American people to allow more Vietnamese to come to this country," said Le Khac Than, who was a car salesman in Vietnam and now works as an insurance agent in Falls Church.

"We are willing to help them get a job, try to arrange for their (house) renting . . . We have had experiences in this country. We have made all the mistakes. The road would be smooth," for the newcomers, Than said.

Speaking from a stage where a yellow light illuminated the South Vietnamese flag, Ngo Vuong Toai, in an emotional voice, told his audience "we must raise our voice to the outside world that the new regime (in South Vietnam) is inhuman." Those in the audience - many of whom were high government officials and military leaders in South Vietnam - raised their arms and cheered.

By contrast, the announced purpose of the day's earlier meeting at the Tenley Cirlce Theater on Wisconsin Avenue was to celebrate Vietnamese-American Friendship Day. Most of the people there were Americans who had protested against the war for years and who have been working for reconciliation with Vietnam since the fighting ended.

Addressing the crowed were such well-known American activists as Cora Wiess, who has been instrumental in sending shipments of food of Vietnam in recent months. Other speakers were David Truong, the former Vietnamese antiwar activist charged with spying for Vietnam and whose trial begins today.

"We are still warring ourselves, within our country," Weiss told the crowd of about 300 people. She accused the United States government of continuing its persecution of Vietnam by refusing to initiate diplomatic relations and to supply aid and by prosecuting former Vietnamese antiwar activist Truong for espionage.

"Perhaps," said Weiss, "vietnam is on trial, too."

The Vietnamese singing before the old flag of the Saigon regime in Arlington were filled with nostalgia for their lost way of life.At Tenley Circle there was another kind of nostalgia, but it, too was fore something that faded away three years ago.

"I know a lot of people here used to be in the streets in the 1960s and '70s," said Miller, "because I was there and I saw you there."