About 100 persons gathered in front of the Russian Embassy in downtown Washington yesterday to mark the beginning of the Jewish festival of Hanukah with a plea for human rights for Soviet Jews.

A few blocks away at Farragut Square, hundreds more listened to representatives of Amnesty International commemorate the 34th anniversary of the signing of the United Nations Universal Declaration of Human Rights.

Intemperate weather kept the crowds from growing to the size that organizers of the events had anticipated, but the speakers were undaunted.

"The day may be cold, but your hearts must be warm for so many of us to get together for this occasion," said Marsha Weinberg, a member of the Jewish Community Council of Greater Washington who organized what was termed a "Festival of Rededication to Soviet Jews."

During the last decade, according to speakers at the Hanukah gathering, over 250,000 Jews have emigrated from the Soviet Union, mostly to Israel.

"Sadly, that emigration has now been forced to slow to only a trickle -- perhaps just 3,000 this year as compared to over 50,000 in l979," said Nathan Lewin, president of the Jewish Community Council of Greater Washington.

At Farragut Square the gathering featured a band of musicians, but it proved less than festive as speaker after speaker -- from places such as El Salvador, Argentina, Chile and South Africa -- recounted instances of kidnaping, torture and murder by government officials of those countries.

Lucia Hamutenya, a Namibian representative to the United Nations, spoke of "slave labor" in her country and how those who fought for human rights were often abducted from their homes and later found dead.

Stuck in the hedges surrounding the park were red placards on which were the names of persons who had mysteriously disappeared. The countries mentioned included Ethiopia, Benin, China, Colombia, the Soviet Union and a host of others.

The rally was organized to draw attention to what sponsors called "continued gross violations of human rights throughout the world."

Amnesty International is a worldwide human rights movement that describes its work as an effort to win the release of prisoners of conscience, meaning men and women detained for their beliefs, color, ethnic origins, religion or language, provided they have neither used nor advocated violence.

Its 1982 Annual Report listed human rights violations in 121 countries during the previous year. "Thousands of people were unlawfully and deliberately killed for political reasons, without any form of legal process, by order of their governments or with their complicity," the report said.

"The extent of the practice and its recurrence in different countries lead Amnesty International to believe that the problem must now be confronted by the international community as a matter of the utmost urgency," the report said.