National Urban League President Vernon Jordan warned yesterday against "a national mood that is turning mean" toward black Americans and he urged President-elect Ronald Reagan to take the lead in fostering a spirit of reconciliation.

The black leader, who was shot in the back on a visit to Fort Wayne, Ind., last May, called 1980 "a year of continued erosion in the black condition . . . a year in which racial tensions increased alarmingly."

With Congress back in session, Jordan protested, "we have senators calling for repeal of the Voting Rights Act, for eliminating public service jobs, for cutting food stamps, Medicaid, urban development programs and others. There are calls to lower the minimum wage. There will be another effort to unconstitutionally prevent the Justice Department from taking part in school desegregation cases."

In terms of racial tensions, Jordan said he saw nothing on the horizon to suggest any improvements in 1981. Instead, he said, there were signs that the situation would get worse under the pressures of growing black unemployment, high inflation and a revival of anti-black feeling.

Jordan delivered his assessment to a crowd of reporters and students at Howard University where he made public the Urban League's annual report on the state of black America. Politically, it amounted to both an appeal and a challenge to Reagan to seek an accomodation with a major statement on racial and social issues.

"If he does," Jordan said, "he will earn the gratitude of blacks and whites who look to the president of the United States for moral leadership. He will have taken a giant step toward ensuring the success of his presidency and the nation's commitment to justice and equality."

In turn, Jordan suggested that blacks, who voted overwhelmingly for President Carter, should stand ready to discuss "feasible conservative alternatives" to existing social programs and problems.

Looking trim and vigorous despite the shooting attack that nearly took his life, Jordan repeatedly claimed to be optimistic about the prospects, but the picture he painted, supplemented by eight reports from black scholars on separate issues, was decidedly gloomy.

"We expect 1981 to be a recession year, with all that implies for record high black unemployment and an already devastated black economy," Jordan said. "Inflation is expected to remain high, squeezing the family budgets of the majority of black people who are poor or moderate-income even harder. Murderous attacks on black people in many cities continue to make headlines. The Klan and similar extremist, racist groups flourish in an atmosphere of revived anti-black feeling."

In defending minority interests, Jordan said it was vital to counter the effects of what he called "the big lie, the big lie that federal and social programs don't work."

"In fact, they do work," he said. "Food stamps have just about wiped out hunger in America. Studies of Head Start programs prove that participating children do better in school than others . . . Other programs have effectively helped millions of people to get productive jobs, decent housing, health care and education."

Neither, Jordan added, was it true that the programs under fire are black programs. For example, he said, the majority of welfare recipients are white; half of all food stamp recipients are white, and four out of five people getting Medicaid and special programs for the aged are white.

"While the vein of racism is taped to generate opposition to social programs, the vast majority of those who would be hurt by cutting or eliminating those programs would be not black people but white people," Jordan said.

At the same time, he acknowledged that improvements are possible for blacks under a Reagan administration if it can fulfill its promises of economic growth for the entire nation. He said the Urban League was also willing to talk with the new administration about such alternatives as urban enterprise zones in depressed areas, an income maintenance system based on a refundable income tax to replace welfare, and incentives for low-income housing development.