AFL-CIO leaders who met here last week at the beachfront resort they have visited annually for more than 25 years made a historic admission of failure and commitment to change.

Yet, the chieftains of the 13 million-member federation also reaffirmed labor's conviction that, despite the worst setbacks in decades, unions and their traditional Democratic allies can make a strong resurgence by changing tactics while sticking to the basic goals embodied in the New Deal.

The centerpiece of labor's reappraisal is a two-year study that some of its authors see as doing for the labor movement what Vatican II did for the Roman Catholic Church in recommending changes and restating goals.

"A major American institution is saying that we failed in some key ways . . . . I am not sure a lot of other institutions have undergone that kind of self-examination," said Thomas R. Donahue, AFL-CIO secretary-treasurer and architect of the report.

"But we are not abandoning traditions; we are saying we have to take a look at new models and old models" for revitalizing organized labor, Donahue said.

The AFL-CIO also hosted former Democratic presidential nominee Walter F. Mondale, who thanked the federation for its unprecedented and controversial early endorsement in the 1984 election. Polls showed that the endorsement hurt labor and Mondale alike by making him appear to be a tool of "special interests."

The 35-member executive council left here apparently convinced that its basic political strategy was sound, however, because roughly 60 percent of AFL-CIO members voted for Mondale.

Labor leaders also said they believe strongly that Democrats should not move to the right, as many suggest, but should stand by the ideals of Franklin D. Roosevelt and John F. Kennedy, Democratic symbols they say were stolen by President Reagan.

The report on the future -- "The Changing Situation of Workers and Their Unions" -- sees the AFL-CIO becoming a catalyst for change within its 96 unions and among 100 million American workers, many of whom are hostile or indifferent to organized labor's message.

Its 28 recommendations include: merging larger unions to increase collective strength, changing bargaining strategies to emphasize arbitration and mediation rather than striking, offering new types of union memberships, strengthening links with community groups, trying new organizing tactics and making better use of the news media.

The key question is whether the AFL-CIO's unions dismiss the report as just another study, officials said, or regard it as a "revolutionary document" and a "historic blueprint" for change -- the phrases used respectively by presidents Albert Shanker of the American Federation of Teachers and Glenn Watts of the Communications Workers of America.

Union membership has fallen from 35 percent to 19 percent of the work force in the last 30 years, and the report warns that the trend could continue because most of the 17 million jobs predicted to be added by 1995 will be in Sun Belt states and service-related industries where labor has a precarious foothold.

"There is a new feeling of looking at all things and all problems . . . to not fight change and look outside" for answers, said Gerald McEntee, president of the American Federation of State, County and Municipal Employees.

Pollsters Louis Harris, Peter D. Hart and others told labor in the report that Americans are "ambivalent" about unions: Workers believe strongly that unions are needed to improve wages and working conditions, but that unions are often undemocratic, heavy-handed in dealing with management and more devoted to the needs of union leaders than of members.

AFL-CIO President Lane Kirkland, in releasing the report, said the polls showed "misconceptions and distortions that are present so widely amongst the public." He said labor will try, partly through increased use of television and other media, to counter the "propaganda" that feeds such negative views.

Fear of reprisals and harassment by employers play a key role in preventing unionization, the study said. It advocated new methods of combating what Kirkland called "ferocious resistance" by employers who often use illegal tactics to stop unions.

Unions win most elections among government workers and have gained more than 1 million such new members, the study said. Unions win these elections, it said, partly because the government usually does not conduct antiunion campaigns.

In private-sector union election campaigns, however, roughly 75 percent of employers hire "labor-management consultant" firms to resist unions, at an estimated cost of $100 million annually.

The report said labor must step up anticorporate activity where necessary, by using the news media and unions' economic clout in such tactics as withdrawing pension funds from hostile institutions.