"For Ronald Reagan, I want to say only one thing," said Emil Farben, 83, in halting English. "When I wake up in the night, I still see the blood running down my son's face, where the SS shot him before my eyes."

The annual gathering of Holocaust survivors is always an "emotional kaleidoscope," as one called it today. For Farben and many others here, it is complicated this year by their anguish over the president's planned trip to the cemetery in Bitburg, West Germany, where some Nazi SS soldiers are buried.

Signs printed hastily in Magic Marker appeared around the Survivors Village at the Civic Center today, urging: "Call the White House. Tell President Reagan, 'Bitburg is not his place.' No honor to S.S. Make one phone call. Tell a friend."

But the gathering's sponsors distanced themselves from such organized protests aimed at the president and said that they had sent a telegram today thanking him for his recent help in evacuating Ethiopian Jews to Israel. They said that they did not want the controversy over Reagan's planned visit to the cemetery to obscure the gathering's purpose or their love for America.

"I am not a man of threat," said Benjamin Meed, president of the American Gathering and Federation of Jewish Holocaust Survivors. "I personally am not going to lead this organization to threaten anybody . . . . We will never be a political organization."

But Menachem Z. Rosensaft, who helped found the International Network of Children of Jewish Holocaust Survivors, called Sunday for death-camp survivors, their children, and American war veterans to "be waiting" for the president at the gates of Bitburg.

Meanwhile, New York City Council member Noah Dear said today that he would be at Bitburg during the president's visit, wearing the striped clothing that had been issued to his father-in-law at the concentration camp at Dachau. He called on Reagan to cancel the trip and said, "I will do whatever I can to embarrass him."

"The young are more radical -- not in the political sense, but in that they feel the pain of their parents," Meed said of the protests. "If we would have to react, we would react against Germany, not America."

In Washington, House Minority Whip Trent Lott (R-Miss.) said that he and other House Republicans believe that Reagan should not go to Bitburg.

"Why should he?" Lott said. "It does have negative connotations . . . . Surely there must be some place more appropriate."

Reagan has added the site of the Bergen-Belsen concentration camp to his itinerary.

Several House Democrats also denounced the Bitburg visit.

"I'm sorry, Mr. President, but you've received bad advice and are wrong to have accepted it," said Rep. John Breaux (D-La.). "Nazi soldiers should not, now or ever, receive a wreath from the President of the United States."

Charles Z. Wick, director of the U.S. Information Agency, said that the "unfortunate" controversy over Reagan's trip is overshadowing the fact that it was "intended as a symbol of reconciliation between two very important allies . . . ."

Several hundred of the 5,000 Holocaust survivors at the three-day conference here attended a Senate field hearing this morning on the search for Josef Mengele, the Auschwitz doctor known as the "Angel of Death." Neal Sher, director of the Justice Department's office of Nazi investigations, assured them that the administration is giving the Justice Department all the resources and support that Sher needs for his investigation.

Dr. Hadassah Rosensaft of New York, an official of the Holocaust Memorial Council, described seeing Mengele knock down a woman who was late for roll call and hold his booted foot on her heart, "whistling an aria from 'Madame Butterfly,' " until she died."

Hans Braun of Westbrook, Ontario, a German gypsy, said that he had seen Mengele dissect the body of a 5-year-old child that Mengele had just killed with a needle in the back.

A twin who had been the subject of Mengele's experiments created a row during the hearing, protesting that "people who have big names get the billing." She was brought on stage and allowed to testify.

Some in the crowd were sympathetic.

"These gatherings are becoming exploited," said Charlotte Rudner of Rockville Centre, N.Y., a death-camp survivor. "Those who have political influence are up front . . . . I know a lot of survivors who are turned off by this."

Officials say that no political influence is involved but that they try to select people with "the greatest symbolic value" for high-visibility events.

The annual reunions of survivors in the United States began in Washington in 1983. An estimated 14,000 attended the first.

Among other things, the gatherings are living testimony that the Holocaust was not, as some revisionists suggest, an exaggeration. Each year brings increased urgency as the number of eyewitnesses to Nazi brutality diminishes.

The survivors' most precious stock in trade is their stories, told and retold to the next generation. At the Farben table in the Survivors Village, Ellen Farben, 25, wearing a University of Massachusetts T-shirt, could recite them along with her mother and father, as if she had been there:

Farben, seeing his son shot by the SS on his first day in Auschwitz and seeing the blood run down the boy's face, as it still does in his nightmares; his daughter, 14, and his first wife killed later in the gas chamber; Ellen's mother, Magda, being forced-marched for 16 days because, even as the war was ending, her SS captors wanted to kill her and the other Jews before they could be liberated.

Like many children of Holocaust survivors, Ellen is aware of special responsibilities and needs.

"Because they lost so much," Ellen said, "I think a lot of expectation has been put on my generation, on me. I think in their own way, my parents love as much as possible, but there is an emotional mental block there. I think, after what they went through, it's very difficult for them to express love."

Her mother and father expressed surprise and sadness at hearing her say this. For adding to their concerns, and for threatening the truth they have tried to build, Magda Farben said of the president: "We will never forgive him."

The survivors' concern about the potential damage of Reagan's visit is great, said Larry Goldberg, director of the sponsoring group.

"But it is one among many strong feelings" he added. " . . . The emotion is almost more than one can sustain."