The last exuberant notes of the traditional Passover songs died away and Marcia Spiegel gave a big kiss of approval to the loudest singer - 6-year-old Renata Sirota.

"That's what it's all for," Spiegel exclaimed with an arm around the child who was one of 19 guests at her Passover seder. "If we don't pass on our faith to the children, then we're in trouble."

Fifteen of the guests were Soviet Jews who have immigrated to the Washington area. Renata, her mother and father have been in this country for about a year and the child has begun to learn something about her Jewish heritage from the Jewish Day School in Rockville, where Mrs. Spiegel teaches. Most of the other guests at the Friday night seder knew little about their religious heritage.

Most, in fact, had never been to a formal seder before.

The traditional ritual of the Passover seder reenacts symbolically the earliest history and faith of the Jewish people Mrs. Spiegel a woman whose religious faith has motivated most of her life, sought to make her seder an educational and religious experience for her guests as well as a pleasant social one.

Her son Marty, 20, a scholarship student at the University of Maryland, easily assumed the role of leader of the family seder, a task thrust on him by the death of his father nearly six years ago. (An older son was unable to return home for the holidays.)

Mrs. Spiegel was everywhere at once - making sure that everyone found the place in the elaborately illustrated Hagaddah, (the printed order of the ritual) she presented to each family, making sure the wine glasses were filled, but most of all, making sure, through translations back and forth into Russian, English, Hebrew or Yiddish, that everyone understood the religious significance of the unaccustomed rites.

Together, mother and son - and daughter Leila, 18 - led the guests through the ancient ritual.

"Blessed be God who has given us the fruit of the vine," translated Mrs. Spiegel after Marty had said the blessing in Hebrew over the first cup of wine.

She passed a dish of minced raw apples, turned brownish with spices and honey, "It's harroset," she explained. "Put some harroset on your matzoh and make a sandwich."

". . . to remind you of the bricks that the ancient Hebrew slaves were forced to make for the Egyptians, interjected Marty Spiegel.

"Passover is not only to celebrate freedom but is also a spring holiday, so we eat eggs," Mrs. Spiegel continued. She directed her guests to partake of the boiled egg before them, dipping them first in the bowl of salt water.

". . . salt, because of the tears," added Marty Spiegel.

She pointed to the extra cup of wine, standing alone on the table and, schoolteacher fashion, solicited from her guests the account of the extra place traditionally set for the prophet Elijah. ". . . And this is for - ?"

"Eleaju!" came the triumphant answer in Yiddish from one of the oldest Russian guests.

"Right!" beamed Mrs. Spiegel. "We always set a place for Elijah. And now Leila will open the door so that anyone who is hungry may come in and eat."

Just where she would have put one more person in her comfortable but modest Kensington home was not clear, but Mrs. Spiegel left no doubt that any hungry stranger who might appear would be welcomed.

Without the mellowing long family memories and tradition, the long seder ritual, which precedes the actual meal, can seem endless. Aware of the strangeness of it all to her guests, the Spiegels shortened some of the parts and skipped others entirely.

But at one point she added a section to the rite in the Hagaddah. Taking up a matzoh - the unleavened cracker-like wafer used to recall the Jews' hasty flight from Egypt that could not wait for conventional bread to rise - she explained: "This is the matzoh of hope for the Jews of the Soviet Union."

Reading the remarks she had written beforehand on kitchen shopping-list paper, she continued, "We know the Soviet Jews are not free to leave or to learn about their religion . . . We are fortunate tonight to have four families with us who have emigrated into the light of freedom."