When Rabbi Marvin Bash calls his twin sons Alan and Jeremy to the pulpit of Arlington-Fairfax Jewish Congregation to begin their bar mitzvah ceremony this morning he will also call on Valerie and Grisha Mendeleyev, also twins, who live in Moscow.

But the Mendeleyevs won't be at the synagogue, and it's unlikely they will ever have a bar mitzvah of their own.

"We're going to call on these two young men to come to the pulpit also," explained Bash, head of the Conservative congregation. "So their voice will not be heard. They will be the Jews of silence."

More than a thousand similar moments of silence, to honor Jews in the Soviet Union who cannot conduct religious ceremonies, have been held during bar and bat mitzvahs throughout the world since 1979 when the Washington Committee on Soviet Jewry held the first "twinning" ceremony. Each time, a Soviet Jew is matched with an American Jew to share a bar or bat mitzvah.

Today's twinning marks the first time in the Washington area that the participants and their absent "twins" in the U.S.S.R. have been actual sets of twins.

A bar mitzvah is a Judaic ceremony that recognizes a youth's formal coming of age into the adult community, usually held as he enters adolescence. A bat mitzvah is the counterpart ceremony for a girl.

There is no evidence, however, that Valerie and Grisha will have a bar mitzvah, or that they even know they will be symbolically recognized at the Arlington synagogue this weekend.

"I met with the chief rabbi of Moscow [Adolph Shayevich] on May 20 while he was visiting Washington," said Rabbi Bash. "He [Shayevich] said he was going to make available to [the Mendeleyev boys] the opportunity to have a bar mitzvah in Moscow." Bash said his sons wrote to Valerie and Grisha in June, but have received no reply.

"It's a completely unpredictable phenomenon as to who receives mail and who does not in the Soviet Union," explained Ruth Newman, executive director of the Washington Committee for Soviet Jewry, established in 1968. "The letter is sometimes delivered to the addressee, but their reply is never permitted to leave the Soviet Union."

Newman said entire adult bar and bat mitzvah classes have been twinned with individuals in the Soviet Union. "There have even been Washingtonians who've gone to Israel to have a twinning ceremony at the [Wailing] Wall" in Jerusalem, she said.

All the Soviet families that are twinned have requested correspondence from the West via relatives or friends who have emigrated from the U.S.S.R., according to Newman.

"In the Soviet Union there is no formal religious education permitted for people of all religions . . . most Jews aren't allowed to have a bar mitzvah," said Newman. Symbolism at twinning ceremonies has included empty chairs with prayer books, flowers and religious garments placed on them.

Jeremy Bash, 13, said when he wrote a letter to the Mendeleyev youths, also 13, "I thought how much opportunity do they have to learn, and how many Jewish friends do they have, which I guess is not that many, and I have so many Jewish friends . . .I think about things like that."

Both Jeremy and Alan said they will write again to Valerie and Grisha to tell them about the ceremony, which about 500 persons were expected to attend.

"I know they have their own dreams and wishes of having a bar mitzvah," Alan said of the Soviet children. "The [twinning] ceremony is just to symbolize that the Jews in America and the Jews all around the world are related as brothers and that we sympathize with what they're going through."