With nearly 2,000 people as witnesses, including two African heads of state, an expedient reconciliation took place in the East Room yesterday. The president and the Congressional Black Caucus made up, with the proper partisan words from the caucus members and with cautious promises and red roses from the president.

"This is the first time a president of the United States has paid tribute to the Congressional Black Caucus," said Cardiss Collins, the chair of the 16-member group, just minutes after Carter handed her a red rose in honor of her birthday.

Yesterday's peace-making session marked the opening of the Caucus' 10th annual legislative weekend In past years the group's relationship with the White House has always added some spice to the political and social treadmill of the two-day meeting Last year as the relationship once again evolved from fair to worse, Collins didn't invite the president to the annual dinner.

This year he apparently stole all the thunder by inviting this important constituency over for beer wine and cake. The formal rooms were so crowded, and the noise of the overflow so loud, that Del. Walter Fauntroy (D-D C) quipped. "This is the Black House today."

This was the same Jimmy Carter whom Collins campaigned against almost up until the last minutes of the Democratic National Convention The same Jimmy Carter who irked John Conyers (D-Mich.) so much, in the heart of the deadlock over the Humphrey-Hawkins full-employment bill, that he stormed out of a White House meeting. The same Jimmy Carter who, days before the Miami riots. Charles Rangel (D-N Y.) thought was "stone-walling" on economic programs for minorities.

"I feel it is imperative that Carter go back," said Conyers yesterday. "Not only would the judiciary be seriously hurt if Reagan was elected, but my work in the Congress would literally grind to a halt." As for Collins, though critics have found her dramatic switch from Edward Kennedy to Carter a weak turn around, she says she feels comfortable with her decision. "I feel what we have said and done in the past has reached his ears and we will keep his feet to the fire.Carter is the best choice Anderson has a record that is just as conservative as Reagan," said Collins Added Harold Ford (D-Tenn). At this stage we cannot afford to send out any wrong signals to black America."

With such political fellowship going on an informality the White House rarely experiences took over. People wandered out to the white-columned portico with their glasses and plates Clusters of consultants lawyers and businessmen sat on the step President Juvenal Habyarimana of Rwanda, who along with Siaka Stevens of Sierra Leone is in the country for the United Nations sessions sought out Coretta Scott King for a photograph Effi Barry the wife of Washington's mayor bottle-fed her infant son and heard a dozen people ask what year he would be running for political office. Bobby Seale the former head of the Black Panther Party, handed out business cards, and offered. "Reagan, Agnew I used to bawl them out. I'm not bawling out Jimmy Carter."

The lighthearted spirit caught President Carter too. As he concluded his remarks on the push for self-determination in Southern Africa and the critical need for a substantial housing and youth employment legislation he shouted. "Coretta Scott King come on up Miss Black America, Miss Wright, come on up.

"These are three of my sweethearts," he said, including Collins "My wife said she wouldn't be back until about 9 p.m. tonight. And she said to give you her best regards. And you can look on the stage and see why I was not concerned that she would be gone."

The reconciliation fever had not snagged Ronald Dellums (D-Calif.), who was the object of a fund-raiser disco last night of the Washington Hilton Hotel. "I guess I really didn't want to go to the White House. The last time I was there the president agreed to meet two weeks later on economic issues and we haven't met yet. I feel I only want to go back for serious work, not a party," said Dellums, one of several Cacus members who didn't attend the Carter reception.

Advertising for the Dellums disco had enticed a couple of hundred supporters with name like Diahann Carroll, Harry Belafonte, Barry White and Ruby Dee Of that caliber only Lou Gossett was visible, but that didn't hold up the business of boogeying.