Walter F. Mondale told labor leaders today that he believes that he lost the presidential election largely because of his failure in "marketing and packaging" himself on television.

In a private 80-minute session with the AFL-CIO leaders who backed him to the end, the Democrat expressed no regrets for his campaign, except for his "failings" as a television performer, AFL-CIO President Lane Kirkland said.

Mondale, according to Kirkland, said "a candidate in this country will have a difficult time unless he gains some mastery over that television tube that dominates public discourse . . . . If you don't know how to use that tool, and use it exceedingly well, you are going to be at a disadvantage."

Mondale "acknowledged what he said were his own failings in grappling with the television medium that clearly is the vital force in public opinion-forming today," Kirkland said.

Mondale thanked the 35-member executive council for the federation's early endorsement in 1983, and said later that he believes that he got a "bad rap" in being labeled a tool of labor.

"I thought that was a bad rap," he told reporters as he hurriedly left a closed-door session. "These are working men and women who are part of this country. They never asked me for anything except for justice."

Mondale's "thank you" visit to the federation's annual winter meeting here comes while Democrats and labor leaders are pondering whether they must change tactics because of President Reagan's 49-state electoral landslide.

But Mondale and the labor leaders who helped provide about $40 million to the party said today that they believe that their problems lie more with the form of their losing effort than with its substance.

Mondale said he believed that he had majority support on controversial issues such as backing a nuclear freeze and freedom of choice on abortions. But those same voters helped to reelect Reagan because of his mastery of the media, Mondale told the group.

Kirkland suggested that Reagan benefited from "clever management by adroit marketers." Mondale, however, was hurt "evening after evening on TV by the spectacle of the Democratic candidates tearing each other apart" during the protracted primary season.

Kirkland said that despite criticism that labor's early endorsement constituted an attempt to control the Democratic Party, the AFL-CIO again would consider using the same tactic in 1988.

But it would be done, he said, only if a Democratic candidate emerges with the support of two-thirds of the 96 unions in the 13 million-member federation -- the number needed to make an official endorsement, by AFL-CIO rules.

Kirkland also strongly criticized Reagan's "dismantling" of the progressive role of the federal government. Reagan believes that the role of government "should be confined pretty much to the raising of armies and the coddling of commercial enterprise," he said.

Kirkland had harsh words for Democrats who have failed to strongly challenge Reagan's budgetary programs.

"Many of the people who call themselves members of the party in loyal opposition . . . are discussing how to outdo the president in cutting and freezing the budget for domestic programs," he said.

Asked whether the AFL-CIO would have been better off backing a more telegenic candidate than Mondale, Kirkland said, "I am not interested in a candidate who's charming and appealing but is empty of principles or of positions that, in our view, reflect the hopes and aspirations of working people."

"We supported Fritz Mondale because we agreed with what he stood for, and we knew that he was a man who wouldn't run away from those things just because it wasn't politically profitable. I would do the same again. We will do the same again."