Even before the White House Conference on Aging, with its expected fireworks over procedures, officially opened today, a mini-revolt occurred last night over the social arrangements.

At the first reception at the Sheraton Washington, scores of the 2,000 guests bitterly complained about the wait to get into the hall, the long lines at the buffet, the cocktail food and the lack of chairs in the hall. "If President Reagan thinks he is doing us a favor by ripping us off of our $22.50 . . ." said a visibly angry Eileen Brookman, 60, of Las Vegas, Nev. "We had to stand in line for 45 minutes before they let us in the door. Then there are no seats, no drinks, not even a cup of coffee. What every senior should do is leave, and leave him looking bad."

The reception was held in a row of exhibition halls, cavernous rooms with tire tracks on black and white checked floors, minimal decorations, and a few chairs and tables. Though the 2,266 official delegates have their expenses paid by the government, the large numbers of observers do not, and several said that last night's buffet of roast beef, shrimp, cheese, raw vegetables and rolls cost about $22.50 per person.

"This is a waste of the taxpayers' money," said one woman, complaining about the entire affair. The Senior Pops orchestra from Long Island played and a sing-along was scheduled, which one delegate found patronizing. "You know what that is? That is ridiculous. They are trying to treat us like children, they think we are senile," said 74-year-old Ruth Scrivner of Belleville, Ill., who had attended the three previous conferences held every 10 years.

When Constance Armitage, the chair of the conference, was introduced, many in the crowd booed. When the brief program ended, Alice Sullivan, 64, of Lafayette, Ind., approached Armitage. "How dare you treat these old people like this," she said, and Armitage answered, "Things will get better tomorrow." Armitage quickly left the room without answering any reporters' questions. As people left the reception rooms, many stopped the conference staff and asked about the eating and social arrangements for the next three days. "No one is going to come if it's going to be like this," said one woman.

The concerns of the delegates were as varied as their buttons, which proclaimed, "Old is O.K.," "Older Is Better" and "Senior Power." Jacob Flisher of Hannibal, Mo., spoke of the housing and transportation needs of the rural elderly and poor; Hattie Derr of Boisie, Idaho, spoke of home health care and Eugenia Evans of Greenwood, S.C., discussed aged widows and health costs. Two years ago Cornelia Curtis of Boston was forced to retire after working 38 years for the state. "I was just getting to be 70, and I retired because a friend of mine had been so upset about her retirement she had a stroke. But the day after my retirement I called the mayor and said I wanted a job. Now I am a secretary to three teachers at a community college," said Curtis, who is also working on college credit and writing four books. Many of the delegates, like Curtis, offered a cautionary attitude about the Reagan administration. "I'm weighing that," she said.

But one issue, the decision by Secretary of Health and Human Services Richard Schweiker that the conference had to vote on the entire set of proposals, not individual recommendations, added fire to last night's annoyance at the reception. James Rua, the deputy director of the New York State office of aging, who was tacking up signs that said "Delegates, do you really have a voice?" said, "We would just like the delegates to make that choice. I see people anxious to get involved in the process and I don't sense a walkout now."