A fundamental but almost unnoticed change has occurred in the U.S. labor movement in the last 20 years -- blacks are now more likely to be represented by unions than whites.

Labor Department statistics show that 33 percent of all black wage and salary workers, including those on farms, are represented by unions, compared to about 26 percent of their white counterparts.

The black union members are found mostly in so-called "second-tier" jobs in the service and garment industries and in nonprofessional positions in the public sector, where pay ususally is lower than that received by union members in "first tier" industrial and skilled trade jobs.

Blacks and "other minorities," for example, make up about 40 percent of the Laborers union, 37 percent of the Service Employees union, 30 percent of the Food and Commercial Workers and 30 percent of the American Federation of State, County and Municipal Employes, the nation's largest public employe union.

And even in the higher-paid unions where salaries often exceed the annual U.S. median family income of $17,640, blacks are making headway. For example, the United Auto Workers union is now 18 percent black.

Labor experts say blacks also are beginning to emerge in union leadership positions, often in second-ranking slots such as secretary-treasurer of a local or international union.

Those experts, for various reasons, contend that the growth of black membership and influence in organized labor is likely to continue.

"If you name any area of union growth today, be it the public or service sector, or the South regionally, it's a place where you'll find large numbers of black workers," said Norman Hill, executive director of the New York-based A. Philip Randolph Institute. The 15-year-old organization, largely funded by the AFL-CIO, is credited with doing much to increase black participation in unions.

Others, like William E. Pollard, director of the AFL-CIO's civil rights department, say the trend probably will continue if racial discrimination continues to decline in the general workforce.

"A lot of what is happening with blacks in unions reflects the hiring policies of management," Pollard said.

The trend has important implications for the future of organized labor.

From one perspective, the development could hasten the day when the U.S. labor movement solves one of its most intractable and debilitating problems -- troubled race relations.

From another view that considers increased competition for dwindling jobs and the growing wage disparity between "first tier" and "second tier" unions, the black emergence in organized labor could spark a renewal of racial bickering.

But most black and white labor leaders prefer to see the trend as a positive development -- one that counters a long-held, popular sentiment that organized labor is, at best, racially insensitive and, at worst, anti-black.

"The people who hold those views are mental dinosaurs locked in the past. . . . They really know nothing about history," said Ernest McKinney, a 94-year-old black labor historian and former union organizer who lives in New York.

Echoing the sentiments of others who agree with him, McKinney added: "There is no way you can equate 1980 unions with those that existed in the early decades of this century."

Then, by rule or practice, many unions excluded blacks. Largely as a result, "You had Negro leaders who went around saying that the white union worker was the worst enemy of the Negro people," McKinney said.

Management groups frequently exploited that sentiment in the early 1900s by using black workers to break strikes by white trade and craft unions.

That practice began to be checked with formation of industrial labor groups, particularly with birth of the Committee for Industrial Organization -- later to become the Congress for Industrial Organizations -- in 1935.

The CIO welcomed black workers, if only as a practical step to end their use as strikebreakers. More progress came in 1955 in the merger of the American Federation of Labor -- the then-preeminent trades and crafts group -- with the CIO.

"The AFL-CIO formed its civil rights department that same year. We let it be known that racial discrimination would not be tolerated in any member union," Pollard said.

In keeping with that stand, the federation's leadership became a major source of support for the civil rights legislation of the 1960s, backing equal employment bills that often were opposed by the AFL-CIO's predominantly white rank-and-file membership.

Those bills, in turn, helped to open jobs previously closed to blacks, and those jobs, in turn, helped to increase black union membership because many of the positions were in "organizable industries," labor experts say.

The changing complexion of the AFL-CIO's membership is an example of that development. Twenty years ago, blacks accounted for about 6 percent of the federation's membership. Today, blacks account for about 2.5 million, a little more than 17 percent, of the federation's 13.9 million members.

By contrast, according to a 1979 Labor Department report on the characteristics of organized employes, blacks constitute 11 percent of all U.S. wage and salary job holders.

"We are becoming a power in organized labor," said Pollard. He said he expects blacks to use that power to push for economic and social changes favorable to black and white union members alike.

Among those supporting the Pollard view is Benjamin Hooks, executive director of the NAACP, an organization that frequently went to court against unions over job discrimination complaints.

"In my own lifetime, I can remember when the chamber of commerce and the labor union were both viewed as antiblack, which I believe they were," Hooks said. But he added that despite his organization's differences with some labor groups, "I believe the labor movement has moved more progressively and faster in supporting the black movement than has any other institution in America."

Blacks now are more likely to join unions than whites because of "organized labor's progressiveness" and because many blacks feel that they only make progress through collective action, Hooks said.

"That's emphatically true," he said. "In the old days, a black on the job was more prone to being fired than anyone else. . . . White workers, at least, had other routes of appeal, going to a white foreman or something, that weren't available to blacks. The black worker felt that collective action was the only way available to him."

Union people say management is well aware of the inclination among blacks to join unions.

Alan Kistler, organizing and field director for the AFL-CIO, told a House labor subcommittee in 1969 about a business consultant who he said advised executives at one seminar not to hire any more blacks than required by equal employment opportunity laws.

"It is my strong finding that blacks tend to be more prone to unionization than whites," Kistler reported the consultant as having said.

"You have to follow the equal employment opportunity laws and have whatever percentage of blacks you are supposed to have . . . But don't be heroes about the goddamned thing. Don't fill up the workforce with blacks. If you can keep them at a minimum, you are better off," Kistler said the consultant told the executives.

In an interview, Kistler identified the consultant as Woodruff Imberman of Chicago, and said he made the remarks at Wake Forest University in Winston-Salem, N.C.

Imberman, reached at his office in Chicago, acknowledged speaking to an executives' seminar at the university, but said he "absolutely did not say those things" attributed to him by Kistler.

But he added, "I do believe that any reasonable person looking back over the last 20 years of our history has to conclude that the only way blacks have made progress is through collective action.The average black tends to believe more than the average white that much is to be gained through collective action. That's self-evident."

Imberman would neither confirm nor deny that he has advised executives to keep black employes at a minimum.

"I tell them to follow EEOC [Equal Employment Opportunity Commission] regulations and to hire qualified people," he said.

Because of the fear that some managers might try again to use race as a tool to divide organized labor, many labor leaders are reluctant to speak about racial percentages in their respective unions. "Some people will use information like that to try to scare whites, and we don't want that to happen," said one black labor official who requested anonymity.

But Sol. C. Chaikin, president of the International Ladies Garment Workers Union, says a greater danger to racial harmony and labor solidarity lies in the widening income gap between the predominantly white "first tier" unions such as those found in the petroleum, steel and transportation equipment industries and the heavily black and minority groups like the Laborers.

Chaikin, in a recent 16-page essay on the subject, called the gap "a generally unanticipated and unnoticed agony within [organized labor's] own family" that could become "a class struggle within a class struggle."

The "first tier" union members generally receive a "total compensation package" -- wages and benefits -- approaching $15 an hour. "Second tier" union members, such as those in his organization, generally get total wages "in the vicinity of 50 to 60 percent of those enjoyed by their first tier counterparts," he said.

Citing a 1979 Labor Department study on employment and earnings, Chaikin said women account for more than 80 percent and minorities for 50 percent of the persons holding the nation's "second tier" jobs. However, he conceded that blacks and other minorities are capturing some of the "first tier" positions in organized industries.

"Clearly some . . . minority union members may be lucky enough to break through into the high-wage promised land of the first tier. For the vast majority, however, the choice is either to make a tough living in the second tier or to make nothing at all," Chaikin said in his essay.

He warned that although "closing the gap between first and second tier workers clearly is in the interests of continued labor unity," that event may not come about because current economic and political pressures may convince the higher-paid unions that their interests are better served by looking after themselves.

Other labor leaders privately dismiss Chaikin's views as alarmist. Others, like Kenneth Young, executive assistant to AFL-CIO President Lane Kirkland, insist that black emergence in organized labor will serve to ameliorate the problems cited by Chaikin.

"This is not to say that everything is buddy-buddy," Young said. "But the labor movement is opening up . . . . Blacks are moving into positions of leadership and are working on problems common to black and white workers . . . . There is a growing respect among the blacks and whites for one another, a respect for workers as workers.

"That's the way it ought to be."