Four thousand flowers from the hands of 4,000 survivors of the Holocaust, placed at the base of the Liberty Bell -- it was a gesture of gratitude, some said today, for the freedom they had found in the United States.

But this year, on what is also the 40th anniversary of the liberation of the concentration camps, the survivors' gratitude was mixed with expressions of what many described as anger and dismay over President Reagan's plan to lay a wreath at the German cemetery at Bitburg, where some Nazi SS soldiers are buried.

In addition, many attending this second American Gathering of Jewish Holocaust Survivors, which began here Saturday night and continues through Tuesday, said they were also upset by Reagan's initial unwillingness to visit a concentration camp, and his comments that German soldiers buried at Bitburg were victims of the Nazis "just as surely as the victims in the concentration camps."

"Forty years after the event, which means in biblical language one generation after, I am afraid we may lose the battle," author and survivor Elie Wiesel told an audience of nearly 10,000 at an "Evening of Commemoration Through the Performing Arts" tonight. "Had our lessons been learned, what happened last week would not have happened . . . This is the beginning, if it is permitted to continue, of the rehabilitation of the SS."

"It was anticipated this event would be an event of appreciation for the liberators," said Menachem Rosensaft, founding chairman of the International Network of Children of Jewish Holocaust Survivors, earlier in the day.

"Instead, President Reagan has turned it into an event where I, for one, am ashamed of the action of the president and his administration. President Reagan does not seem to understand. Reconciliation at the expense of remembrance is not an acceptable way to go. It will send out a message that 'yes, it's true there are some Jews concerned with the Holocaust, but this really isn't a priority of ours.' "

Rosensaft is the child of two survivors and was born in 1948 at the displaced persons camp at Bergen-Belsen, the site of the former concentration camp that the White House announced Friday Reagan will visit.

Today, Rosensaft spoke downtown at the Memorial to the Six Million Jewish Martyrs. The crowd of about 10,000 listened as several clergymen and Philadelphia Mayor W. Wilson Goode promised again and again, "We will never forget." They also listened as speaker after speaker condemned Reagan's itinerary and his words.

Then they rose and walked the 14 blocks to Independence Hall. Tiny, withered old women went arm in arm with their tall, robust daughters and sons, and before them singing children carried signs with the names of the towns and concentration camps where Jews lived and died. Kiev, Lansberg, Amsterdam, Czernowitz, Nuremberg.

Over the next two days, the participants in the gathering will attend symposiums on such subjects as "The Abandonment of European Jews During the Holocaust," "Bringing Nazis to Justice," and "Telling the Next Generation." Tonight they attended the performing arts program presented by the U.S. Holocaust Memorial Council, in which Wiesel, actors Ellen Burstyn and James Earl Jones, TV correspondents Mike Wallace and Barbara Walters and others participated.

The Senate Judiciary Committee will hold a special subcommittee meeting here Monday morning, chaired by Sen. Arlen Specter (R-Pa.), on the search for Nazi Dr. Josef Mengele. And when the survivors have free time, they gather at the "Survivors' Village," an expanse of tables in a cavernous Convention Center hall where they can, as they did in Washington two years ago, and in Jerusalem, at an international gathering of survivors two years before that, meet and talk.

This time the talk is, according to Benjamin Meed, president of the American Gathering, "90 percent" about Reagan's visit to Bitburg. The outrage, however, is qualified.

"This is still the president of the United States," Meed said. "We live in the country where we can say to the president we do not agree with him. We could never have done this in many of the countries of the world. But we cannot give up any principle for any expediency.

"We are upset. When you are being misunderstood by an enemy, you take it for granted, but it is very hard to be misunderstood by a friend.

"There are 200,000 survivors in the world," he said. "I have to put it in hard language. How many Germans sleep today on mattresses which are still filled with Jewish hair? How many Germans adorn their houses with art confiscated from Jewish homes? We are pleading with the president to understand."

Frank Morgens of New York City, who escaped from the Warsaw ghetto with his wife and children aided by a Christian woman, said, "We have a feeling for survivors. We are like brothers and sisters."

Morgens and his wife Marie sat at one of the Survivors' Village tables early in the day. The huge hall echoed with the plaintive voices of people still looking for relatives and friends. "I would appreciate it if someone could tell me they know something about my little sister," one man sobbed into the microphone. "Please, if someone could help me . . ."

Like many others interviewed at the gathering, Morgens said he was deeply disturbed by Reagan's plans. But, also like many others, he sought to avoid condemning Reagan, whose picture hung next to Jimmy Carter's at the entrance of the hall.

"As far as Reagan is concerned, we consider him a decent person and devoted to the care of the memory of the survivors," said Morgens. "I have nothing against the younger German generation. However, any time I meet a person over 60, I am thinking he was the killer of my father. I behave toward that person with reserve. Not with hostility, because I do not believe in collective responsibility, but with reserve."

Henia Ring Schiff of Duncan, Okla., wore a sign on her chest -- "Is anyone from Krzepice Poland?" -- and said she hoped to find someone from the town where she lived as a child before she was taken to a series of concentration camps, including Bergen-Belsen. She is the only survivor of her family. Now she is married to Max Schiff, an American who fought in Germany during World War II. He helped her write the letter to Reagan telling him of her distress.

"It took me three days to write that letter," she said. "Bergen-Belsen -- I'm glad he's going there, but if I had to choose between him not going to Bergen-Belsen so that he would not go to that cemetery . . ."

Her voice trailed off.

In the last few years, the children of survivors, often called the second generation, have formed groups to discuss what happened to their parents and how it has been handed down to them. Many of the participants at the gathering are second generation. The pain may be inherited rather than directly experienced, but a number said it has marked them nonetheless, and so they shared the general distress over Bitburg.

"He just doesn't really have feelings about it," said 25-year-old Barbara Ann Reich of Rye Brook, N.Y. Reich's mother was in a labor camp in Romania at the end of the war. "It also shows the ignorance of the whole administration. They really should have loyalty first to the Jewish population before they care about the Germans. It's very distressing to see. You really feel more alienated -- because of the president's action -- from your whole country, and you feel all the more reason to work for Israel."

Even before last week, the survivors' gratitude towards the Allies was scarred by another wound. As author and survivor Vladka Meed told the crowd by the memorial, "The world paid attention only to the military battle, not the battle against the Jews. The gates of America and Palestine were kept closed."

"If they had even bombed the rail lines, slowed it down for a few days, they could have saved thousands," said Anton Segore of Albany, N.Y. "They were burning 6,000 an hour at Auschwitz. They could have bombed the camps. People say, 'That would have killed the prisoners,' but at least they would have died in dignity."

However, Segore said, "I don't feel any bitterness. I am a veteran of the Korean war. I am a proud American."

But then he added, "If I were Elie Wiesel, I would never have accepted that gold medal," referring to the Congressional Gold Medal Wiesel received from Reagan in a dramatic ceremony on Friday. "I was liberated with Wiesel. I feel he should not have accepted it."

Then a smiling man who had been standing nearby approached Segore and gave him a pat on the back.

"I was liberated with this guy," said Josef Schwartz of Philadelphia. "April 15, 1945. We didn't see each other for 40 years, and then today! I recognized him."

Schwartz patted Segore again and the two men walked off together.