Walter E. Washington agonized for months, his friends say, over endorsing a candidate in the race for mayor. Early on, when a host of would-be's courted his favor, the former mayor delighted in the notion of being a power broker. Easier said than done.

To endorse someone openly might bring his own record back into public debate, Washington was told. Was that what he wanted? Well, someone then suggested, why couldn't his wife Bennetta, a pillar in some parts of middle-class black Washington, make the endorsement? But was that what he wanted?

In the end, Washington quietly made a few telephone calls to contributors on behalf of lawyer Patricia Roberts Harris, who wound up losing soundly to incumbent Mayor Marion Barry in last Tuesday's Democratic primary.

Then there was Sterling Tucker, the former City Council chairman. First, he considered running for mayor, as he had done unsuccessfully in 1978, but decided against it. Then he considered a race for an at-large seat on the council, and decided against that. Finally Tucker launched a last-minute campaign to recapture the council chairman's seat, and lost.

On the surface, Washington and Tucker were little more than footnotes to last week's primary election, which marked the triumph of the District's first modern-era political organization, headed by Barry.

But their failures also reaffirmed the eclipse of the city's old political order -- old-line, moderate blacks who gained much of their initial prominence through appointed positions and were longtime trusted friends of the city's business community.

The new order -- younger blacks and whites who have only recently earned the respect of city business leaders -- has brought to the city a new style of activist politics honed in numerous quasi-political community action battles of the 1960s.

"It is a government of issues and people, not colors and cliques," said Phil Watson, a new breed political observer who this year ran housing activist Marie Nahikian's unsuccessful campaign for City Council in Ward 1.

"The people who were the outsiders for so long have out-organized the old insiders who became complacent," Watson said. "Look at Barry and Clarke's campaign. They had a lot of people working for them and they reached a lot of people who now feel a part of their group."

Sharon Dixon, Harris' campaign director, said Washington's decision to stay out of the race signals a change in city's politics from the time when Washington could be a force in city politics primarily because of popular support.

"All Walter Washington had to call upon was long associations and political associations. His only calling card was respect people had for him or for Pat Harris. But that time has gone," said Dixon, one of those who sought Washington's endorsement of Harris.

"This used to be a sleepy Southern town where the politics was based on friendship and rapport carried the day for a politician," she said. "Now we have seen where it's the bottom line of what can you do for me that carries the day . . . It has to do with the incumbent granting or denying favors. Walter Washington has nothing to offer."

Washington, 67, a lawyer and life-long bureaucrat, rose through the ranks to become executive director of the old National Capital Housing Authority. President Johnson named him the city's mayor in 1967, and he held the appointive office for seven years before he was elected to one term in 1974.

Tucker, 58, who for 22 years was executive director of the Washington Urban League, was appointed to the City Council in 1967 and in 1974 became the city's first elected council chairman.

By contrast, many of the new breed in control, including Barry, Ivanhoe Donaldson, the mayor's highly influential campaign manager; Frank Smith, a school board member who won nomination to the city council last week, and City Council member John A. Wilson (D-Ward 2), came from the ranks of the Student Non-Violent Coordinating Committee (SNCC).

Council member David A. Clarke, who won the nomination for council chairman, is a former member of the Southern Christian Leadership Conference.

Tucker shared their concerns about civil rights, but found their brand of activism too narrow and doctrinaire for his taste. He preferred to mix street activism with quiet diplomacy behind the scenes. "My kind of activism was a little broader in span," Tucker recalled recently.

Washington was even less prominent in civil rights activism than Tucker, preferring instead to see his contribution as patching up race relations in the city after the 1968 riots and providing a kind of steady, unthreatening leadership at city hall that would pave the road for home rule.

Washington, who now practices law, virtually dropped out of sight after he and Tucker lost to Barry in the close 1978 Democratic mayoral primary. He seemed anxious to put his final months in office behind him -- a period that was marked by minor scandal and persistent criticism that he was an inept administrator.

But after three years of relative obscurity, he happily reappeared late last year and encouraged speculation that he might serve as a power broker in the upcoming race for mayor.

A reception held in his honor last November at the Four Seasons Hotel in Georgetown attracted the cream of the city's political, labor and business community, including Barry, his erstwhile opponent and critic.

"I'm not trying to offer myself as a king-maker -- just a good citizen," Washington explained at the time.

After Harris entered the race for mayor in early April, her top aides repeatedly leaked word that Washington was in their corner, but that he was reluctant to make a public endorsement.

Several of Washington's former supporters assisted Harris' campaign. James L. Hudson, a lawyer and vice chairman of Washington's 1974 campaign, was a key adviser on organizational strategy; Charles T. Duncan, who served as corporation counsel when Washington was mayor, was campaign treasurer; R. Calvin Lockridge, a member of the school board who helped direct field operations for Washington's 1978 campaign, supervised Harris' field operations.

An aide to Barry said last week he wasn't surprised by Washington's decision to stay out of the race.

"Walter in his own mind wants to be an elder statesman and wants to stay above the crowd," the aide said. "Unless he had come out publicly, his making a few phone calls was irrelevant."

Four years ago, after narrowly losing to Barry in the Democratic mayoral primary, Tucker was a bitter and dejected man. Last Friday, in the wake of his second major defeat which, even he agrees, has probably put an end to his political career, Tucker seemed philosophical and even optimistic about the future.

Sitting in a conference room of his consulting firm office on Connecticut Avenue NW, Tucker expressed grudging admiration for Barry's smoothly operating organization, which helped defeat Tucker by providing Clarke with campaign workers and helpful polling data.

"I got hit by the Barry express," Tucker said, with little hint of bitterness. "What we have here for the first time is a strong political organization."

"Having a good political organization is a good thing," he added. "But what one wants to guard against is having a political machine."

Tucker said he intends to keep his hand in civic activities, but he said he feels that he has finally lost his appetite for elective office.

"One should never say never, except 'never say die,' " Tucker said. "But the likelihood of my running again is about as close to zero as you can get."