For the captains of organized labor, their most ambitious and costly political adventure has turned out to be a bonding experience akin to being the best bailers on the Titanic: It has left them internally more unified and strong, they say, but locked in a grim, defensive struggle against a conservative, anti-union tide that has swept up many of their members.

Stoic union leaders stood united behind AFL-CIO President Lane Kirkland and their presidential candidate, Walter F. Mondale, the day after his overwhelming loss, as they had throughout the arduous campaign year.

"The AFL-CIO remains undaunted," Kirkland said in a statement expressing pride in the federation's performance in carrying out its unprecedented strategy of endorsing a "solidarity candidate" before the first primaries and caucuses.

The unions "delivered" their vote, in the sense that a majority of union households gave their support to Mondale, and their support far exceeded that of nonunion voters.

In one typical nationwide exit poll, taken by ABC News, union households favored Mondale over President Reagan, 53 percent to 47 percent, compared with a nonunion vote of 34 percent for Mondale and 65 percent for Reagan.

Polls by all three networks showed that union households voted for Mondale-Ferraro by 17 or 18 percentage points more than all other households.

An independent poll of AFL-CIO households (excluding independent associations and unions such as the Teamsters), which was commissioned by the federation, raises that differential to 20 points, Kirkland said.

And when AFL-CIO union members alone were polled, as opposed to their entire households, they supported Mondale by 60 to 40 points over Reagan.

The union message was especially well-received among unemployed voters, who voted for Mondale by nearly 2 to 1.

But the union vote fell short of the traditional target of 65 percent support for labor's candidate among union members -- the proportion officials say is typically needed to offset the conservative tilt in the rest of the electorate.

"We were bucking a tremendous tide," said Rachelle Horowitz, political director of the American Federation of Teachers.

"I feel like the guy standing on the bow of a ship spitting into the wind," said Robert A. Georgine, head of the AFL-CIO building and construction trades department. "There are a lot of questions in my mind as to whether we don't find ourselves talking to each other -- that is, the different levels of leadership -- and not conveying our message to the membership at large."

Because of the pains Kirkland took to build a consensus for the early-endorsement strategy among the usually querulous union chieftains, his status as their leader emerges unscathed, by all accounts.

"He solidified the labor movement and held them together. That's not easy," said William H. Wynn, president of the federation's largest union, the United Food and Commercial Workers.

Even some top labor officials who had been reluctant to enter the process said yesterday that, if they had it to do over, they'd endorse early and they'd endorse Mondale. "I have no regrets," said one. "We learned some things."

Many said the enthusiastic response of their local officials and activists this year contrasted sharply with 1980, when no amount of urging from the top could motivate the troops to work for President Jimmy Carter.

After months of telling their members how awful a second Reagan term would be for working people, the labor leaders yesterday were trying to look on the bright side.

They helped the Democrats battle Reagan to a standstill in congressional and gubernatorial races, they said, and they expect the president's influence in Congress to be weaker in his lame-duck years. As for his political appointees at labor-related agencies, said one, "They can't be worse than they've been."

Today, the federation's political team is meeting to sift evidence from around the country showing how their retooled machinery performed. But some of the lessons of 1984 are clear.

"We've just got to do a better PR public relations job," with union members as well as the general public, said Joan Baggett, political director of the Bricklayers union.

Many union members apparently "are not making that connection between the labor laws which unions say Reagan has moved to weaken and their pocketbooks."

As for unions' public image, Baggett added, "I don't think any of us was prepared for the beating labor took, the vehemence of it, in the primaries."

Labor became an issue during the primary fight between Mondale and other Democratic contenders, most notably Sen. Gary Hart (D-Colo.). By spring, even some labor leaders were complaining that Mondale had failed to put enough distance between himself and them to cast off his image as a captive of special interests.

"I guess we never did get our point of view across that we're not a special interest and that it really was the rank and file pulling the load," said Phil Sparks, a spokesman for the American Federation of State, County and Municipal Employes. "Our union had 25,000 rank and file working on Election Day for the ticket, and you can't order people to do that. They have to do it on their own."

While labor officials braced for a bout of scapegoating and finger-pointing from their critics, they had a few complaints to aim at the Mondale campaign. "While we were talking to our members the best we could, the national campaign was not reinforcing our message" about basic Democratic themes until the final weeks, Sparks said.

Wynn, echoing numerous Democrats, said he wishes Mondale had not said he would raise taxes. "You don't have to be dishonest," he said, "but you don't have to tell 'em everything."