The National Urban League, which yesterday ended its annual conference here, has had image problems during the last couple of years. When the mammoth 1983 March on Washington marked the 20th anniversary of the historic march led by the Rev. Martin Luther King Jr., the Urban League decided not to participate. When the Rev. Jesse L. Jackson launched his historic bid for the Democratic presidential nomination, the League's leadership was conspicuously missing from the ranks of his supporters.

These seemingly timid public stances are in marked contrast to the League's more virile public image of earlier days. But while the organization may not be in the vanguard of new and dramatic thrusts and may need redirection, nobody questions the strength of its annual "State of Black America," which is considered the nation's most authoritative black status report.

Begun 75 years ago to take up the cause of poor blacks when both government and the private sector would not, the League by the 1960s had become a conduit for delivering federal services to the poor. Indeed, two of its most dynamic leaders, Whitney Young, in the 1960s, and later Vernon Jordan, worked hand in hand with Republican and Democratic administrations to help poor blacks. Although the Reagan administration slowed government funding to a trickle, the League has used its limited budget to implement job training programs, stimulate minority business and deliver services through 113 local affiliates.

Despite the efforts of the League and other civil rights organizations, many people believe that a leadership crisis exists in black America and that the League has become too cautious and has lost credibility.

"The Urban League movement has been serving America for 75 years. And in all that time there has never been a moment when someone, somewhere, wasn't complaining about us," said League President John E. Jacob. "That's because we were doing our job."

However, the question remains: Are the League's programs, tactics and strategies relevant to the problems blacks face today? I'd have to say yes and no.

If its convention is any example, organizationally, the League may be the best run of all the civil rights groups. The conference, which closed last night at the Sheraton Washington Hotel, attracted about 10,000 people, many of them middle-class blacks who use the convention as a networking opportunity. Hundreds of exhibitors were on hand, many of them recruiting through the League's Job Bank. In the midst of Tuesday's program, about 1,500 conventioneers marched on the South African Embassy.

Many League leaders shared their enthusiasm about such local programs as the Miami League's $29 million housing project for the elderly, and others noted Betti Whaley of the District as typical of the League's dynamic local heads.

In workshops that examined the League's new focus on teen-age pregnancy, male responsibility for pregnancy and child rearing, and households headed by single females, the League tried to shake its elitist image by mixing academics and grass-roots people.

"Calling the children of single mothers 'illegitimate' and their homes 'broken' adds to the destruction of black families, rather than supporting them," Daphne Busby of the Sisterhood of Black Single Mothers told one forum.

But the Urban League, like many other organizations, also suffers shortcomings. It lacks a broad nationwide program that would attract new members, especially those in the 25- to 50-year age group. Its multiple programs, ranging from crime prevention to preparing young people for skilled jobs, may have the effect of diffusing its efforts and minimizing its overall impact.

The League also needs to recruit more members to improve its financial situation and refocus its mission to address issues that are important to middle-class blacks, including the millions who now work in corporations and whose stresses and concerns are being overlooked by traditional organizations. In this vein, one consideration should be improving the black community's understanding of mass media practices.

Although its recent cautiousness has cost it credibility, when the accomplishments of the last 75 years are weighed against the shortcomings, the conclusion has to be that America is better off for having the Urban League.

But only leadership, dynamism and vision will make it as relevant in the future as in the past.