"We survived Nixon, we can survive Reagan," National Urban League president Vernon Jordan said wearily yesterday.

On the morning after, black leaders across the nation read over Tuesday's election returns with foreboding and alarm -- their friend in the White House resoundingly defeated; many old and trusted allies on Capitol Hill, now gone.

"We're in mourning in Detroit," said an aide to Mayor Coleman Young.

As they had four years ago, blacks gave Carter 80 percent to 90 percent of their votes Tuesday. But this time it was not that critical margin of difference they had been so proud of before. This time it was a mere statistic for the chapters in the almanac recording the great conservative tidal wave of 1980.

"There is the sense of being stunned that sort of permeates the black community," said Eddie Williams, head of the respected black think tank, the Washington-based Joint Center for Political Studies. "I think there was a general belief that it would be a cliffhanger of a race. It was not that at all, it was a landslide. . . . When you consider that in the climate we're in -- rising violence, the Ku Klux Klan -- it is exceedingly frightening."

"We've suffered a very definite setback," said NAACP executive director Benjamin Hooks. "We simply have to rearm and reorganize. I suspect that black people across the nation will recognize that we're really in a hard fight.

As the stock market soared and there was a feeling of euphoria elsewhere, there was the sense, black leaders said, of once again being alone. Jews and labor had deserted the Democratic president in sizable numbers and the old New Deal coalition, strained in recent years, was now seen as being in tatters.

"We [blacks] were the only members of the traditional Democratic coalition who remained true to the coalition. Everybody else abandoned it," said Jordan.

Everywhere there was a search for some definition of the true consequences of the changes in the White House and in the Senate. Mayor Ernest Morial of New Orleans issued a gloomy message to residents of his city, noting, among other changes, that Republican control of the Senate would mean less influence for Louisiana's two once-powerful senators.

"It is certain that our citizens will o longer have a great influence in the deliberation of the Senate that we now enjoy," Morial said.

Jordan said he thinks that abortion, child health insurance programs and gun control legislation all are threatened.

"I don't see any new, innovative things happening in welfare reform, but I don't see any retreat from where things are at present," he said. "When the conservative senators look at it for what it is, they're going to find that 65 percent of welfare recepients are white."

"I think it's also important to dispel the notion that because black people did not vote for Reagan, they will not benefit from whatever positive are put forth. . . . If you take Mr. Reagan at his word that he is going to put America back to work again, he can't put just white people back to work."

Operation PUSH director Jesse Jackson, who had flirted with Reagan in early August, threatened a walkout on Carter at the Democratic National Convention a week later, then ended up as one of the most ardent campaigners for the reelection of the president, was the most bitter of the black leaders who were interviewed.

"Reagan basically offered [his supporters] a return to the good old days and racial security -- security from the strikers, the blacks, the rebellious women and a willingness to use macho and manifest destiny in foreign policy," he said. "A mood in the country was conjured up.

The NAACP's Hooks said black leaders would seek a meeting soon with Reagan to present him, as they had presented Carter four years ago, with an agenda of programs and policies desired by black Ameicans. But attention was being given yesterday to setting up quickly a meeting just of black leaders themselves.

During the carter years, as black mayors and civil rights leaders gained an unusual degree of access and influence at the White House and in the halls of government, there had also been competition and disagreement over strategy, policy, appointments, and jealousies over who was to get credit for initiatives, who would get airtime on the network news.

Yesterday there was a strong feeling that those differences now must either be thrashed out and resolved behind closed doors, or put aside. And, here and there, were a few brave stirrings of optimism about battles against the conservative tide in the days ahead.

"We tend to do better in adversarial situations than we do in a friendly situation," Jordan said.