Saying it was "time for change, personally and institutionally," Vernon Jordan formally announced his resignation as president of the National Urban League yesterday.

Jordan said he plans to leave the top job of the civil rights group at the end of the year and confirmed reports that he will join the oil and lobbying powerhouse Washington law firm of Robert S. Strauss, former Democratic national chairman.

Announcement of his departure set off immediate speculation about his successor. Some of the names mentioned included Jordan's deputy, John Jacobs, Washington lawyer Ronald Brown, outgoing Atlanta Mayor Maynard Jackson and former United Nations ambassador Andrew Young, who is in a tight race to succeed Jackson at Atlanta's city hall. University of the District of Columbia president Lisle Carter, the head of the league's search committee, declined to discuss names of persons being considered.

Though announcement of his resignation came unexpectedly, Jordan's close friends said they were not surprised that he had decided to leave the high visibility and pressures of the civil rights post for a more private life.

"Vernon basically said 10 years was enough time for anybody to be at the league," said New York lawyer and longtime Urban League board member Charles Hamilton Jr.

"People have only a sense of the glamor of the Urban League, but basically your life is spent between Peoria and Minneapolis" speaking to affiliates, said Jordan's close friend and colleague Eleanor Holmes Norton, former head of the Equal Employment Opportunity Commission. "I think it's a stunningly burdensome job that has few high moments and many pressures."

"Vernon wants a life that is slower paced. It's been grueling," she said.

At a news conference in New York yesterday, Jordan, 46, said he just felt that it was "time to turn to new fields and new endeavors," noting that since his graduation from Howard University Law School in 1960 the civil rights movement had been "my vineyard," as he moved rapidly upward through positions with the Southern Regional Council, the Office of Economic Opportunity, the Voter Education Project, the United Negro College Fund and at age 36 to the top job at the league.

He dismissed press speculation that continued health problems from a sniper bullet wound were the reason for his resignation. "I feel absolutely fantastic--I play tennis three times a week," he said.

Nor did he leave, he said, due to any image problem from being with a white woman when he was shot.

"No, of course not...not my problem," he said in response to questions.

Articulate and polished from his pinstripe suits and rep ties down to his argyle socks and Gucci loafers, Jordan sits on the boards of major corporations, and counts senators and captains of industry among his personal friends. He, alone of civil rights leaders, was included among the grandees invited to the fashionable parties in Georgetown and Manhattan for Ronald Reagan before the inauguration. But, Jordan has said, his advantage in having access to the new administration has not meant comparable influence over White House policies.

His friends have stressed the importance of Jordan's ties to power and said they have aided him in raising private contributions for the league in his unique position as broker between the civil rights movement and Establishment America. They also credit him with bringing tighter managment to the league and substantially increasing its funding.

But his critics, and there are several, are offended by his imperial style, contend that he has on occasion altered positions so that he would not offend contributors, andsay he has presided over an organization more intent on garnering benefits for the black middle class than the poor.

Robert Woodson, a former Urban League staffer, left the organization dissillusioned a few years back and joined the right-of-center American Enterprise Institute, where he is the only black fellow.

"Many of the goals pursued by the Urban League were more beneficial to middle-class blacks and that's fine. But I think it's a mistake to assume that affirmative action helps the poor. They've got to address some of the fundamental economic problems," he said.

Under Jordan's leadership, federal support for the league and its 118 affiliates grew to more than $110 million. Now, with the Reagan budget cuts, the league stands to lose most of that. There have been layoffs at league headquarters in New York.

In an interview at the league's annual convention here in July, Jordan spoke about the plight of young middle-class people being laid off, guessing that the cutbacks would be harder on them psychologically than on street youth long out of work.

But, he suggested to the heads of the league's affiliates, the cutbacks could be a "blessing in disguise" for the league.

"For the first time in recent memory, the movement will indeed need to act like a movement," he told them. "We will need to develop new solutions to old problems, and in some instances to return to less glamorous approaches to the delivery of human services."

That now becomes the burden of his successor.