A week ago, the precinct captains in the 41st Ward Democratic organization told Alderman Roman C. Pucinski that they wanted to do the once unthinkable: endorse a Republican candidate for mayor.

Pucinski, a former mayoral candidate, hesitated.

A ward boss for 22 years, a member of Congress for 14 and alderman for the last 11, Pucinski hasn't survived by being foolish.

"I sent them back on the streets to talk to their constituents and make sure this is what should be done," he said today.

Meanwhile, Pucinski took a little poll.

He asked 200 voters in his predominantly white ward on the northwest side of the city whether they preferred Republican Bernard E. Epton or Rep. Harold Washington (D-Ill.), the Democratic nominee. About 90 percent said Epton. The 78 precinct captains came back with the same message, Pucinski said. "They were unanimous that we endorse Epton."

The 41st Ward organization, the third largest in the city, did just that. And Pucinski Thursday night became the eighth Democratic ward committeman here to endorse Republican Epton instead of Washington, his party's first black mayoral nominee.

"I think the bloom is off the rose for Washington," Pucinski said. "He has persisted in his campaign of confrontation politics, and it isn't working."

Of the 50 Democratic ward committeemen in the city, 29 have endorsed Washington formally and eight have endorsed Epton formally.

The eight ward bosses include some of the best known cogs in the city's old Democratic machine.

One is Alderman Vito Marzullo, dean of the city council and a member of the Democratic organization since 1919. Another is park district superintendent Edmund L. Kelly, who controls about 3,400 patronage jobs, the most in the city government.

They said they deserted Washington out of a combination of self-preservation, personal pique and misgivings about the Democratic nominee and racial politics. They said they all believe that one of the great secrets of political leadership is to know when not to rush to the front of the parade.

They see Washington as a threat to them because he advocates doing away with the patronage system, the life blood of the machine. He also says he wants to abolish the park district, which would mean an end to Kelly's patronage jobs and his power base.

"Washington has committed himself to destroying the organization, destroying the machine. Why should we let him kick us in the teeth?" Pucinski said.

He charged that Washington also ignored the niceties of machine politics. The same night that Jane M. Byrne beat the machine four years ago, Marzullo recalled that she telephoned him at 11:30 p.m. and said, "Vito, we've got to get together." He became a Byrne ally.

Washington never called Marzullo or many other Democratic leaders, and by the time his campaign got around to attempting to rally Democratic regulars it was too late for many.

This left a bitter taste for those like Marzullo.

"I'm 85 years old," he said. "You mean I should take orders from somebody like that who won't pay me the time of day? I'd go back to Italy first."

Aided by a host of national Democratic politicians, Washington has belatedly tried to unite the party and has had some success. On Wednesday night, he raised $550,000 at a unity dinner, the largest such event for a non-incumbent mayor in the city's history.

But Pucinski charged that Washington and many of the national Democratic figures who have campaigned for him have stirred up racial tension in the city.

"There's no question that this city is torn apart like it's never been torn apart before," he said. "And it's Mr. Washington's fault. He's been lighting matches all over the place and then he shouts fire. He made race the issue."

In a television interview taped for broadcast this weekend, Washington, however, continued his attacks on Epton, calling him a "masterful whiner" who has "unfairly maligned me." His new television ads depict Epton as a puppet whose strings are pulled by President Reagan.

Washington also lashed out at suggestions that he had contributed to racial tension.

In a separate appearance on the same show, Epton pledged to appoint several blacks to key city posts if he is elected.

"Whoever is elected mayor will have to prove to the nation that Chicago isn't a racist city," he said.