Big Labor has joined Big Business in the hunt for merger and diversification.

Like business, labor's search is influenced by the desire to increase power and holdings and, ultimately, to survive.

Also, like business, labor's mergers and conquests of what one AFL-CIO official called "virgin territory" have produced some curious offspring.

A trucker's union represents police officers, a bakers' union now includes tobacco workers and an organization of chemical workers has taken chicken cleaners and cutters unto its bosom.

The merger/diversification movement grows stronger as unions try to cope with double-digit inflation, increased membership demands for technical and legal assistance, business opposition to union growth in some regions and a national shift from a manufacturing-based economy to one dominated by a largely white collar service sector.

For example, a decline in steel production, accompanied by the loss of thousands of workers, has prompted the United Steelworkers to look for new members among clerical and professional workers.

"There's a lot of room for union development among those people," said a steelworkers spokesman, whose 1.2 millin-member union is about to complete merger talks with the 20,000-member Insurance Workers International Union.

The spokesman said the merger would give USW "a foot in the door, as far as jurisdiction is concerned" in the nation's financial industry.

"Once you've got jurisdiction, your talent and willingness to go out and organize will take you as far as you want to go," the spokesman said.

Before being wooed by the Steel-workers, the IWIU held merger talks with the 98,500-member Office and Professional Employees International Union -- an allied group that, presumably, better understands insurance employes.

BUT IWIU President Joseph Pollack said his members wanted as much financial and organizational clout as possible in dealing with the constantly changing insurance industry, and decided the Steelworkers could better defend their interests.

"It'll be of great benefit to the both of us to get together," Pollack said.

About 109 unions and professional associations have gotten together in 64 mergers since 1955, when the American Federation of Labor merged with the Congress of Industrial Organizations to form the AFL-CIO.

Since its inception, the federation has pushed merger and diversification as ways to eliminate overlapping jurisdicitions of unions that belonged to the two old groups. AFL-CIO President Lane Kirkland said the strength of organized labor depends on continuation of that process.

"Every merger broadens and strengthens the entire labor movement," Kirkland said.

"The trend is toward fewer, stronger, and more diversified unions, and the AFL-CIO encourages that trend," he said.

Thirty-six of the mergers occurring in the last 25 years took place between May 1956 and June 1971, according to the Division of Industrial Relations in the Bureau of Labor Statistics.

Twenty-eight union mergers occurred between July 1971 and February 1980. Most of the mergers were between AFL-CIO affiliates.

However, it is a nonaffiliate of the AFL-CIO, the 2.3-million-member International Brotherhood of Teamsters, that has proved most adept in absorbing smaller unions and moving into areas outside its original jurisdiction -- trucking.

When it was organized in 1899, delivery trades workers accounted for all of the Teamsters membership. Today, truckers and haulers make up barely 25 percent of Teamsters members. The other 75 percent comes from the ranks of the nation's police and fire departments, hospital workers, editorial employes and other fields that have little or no relationship to trucking.

The Teamsters were kicked out of the AFL-CIO in 1957 on grounds the union refused to cleanse itself of alleged corrupt leadership. But now, largely because of its organizing ability and a renewed quest for labor unity, the Teamsters have been invited to rejoin the federation.

Last week, Teamsters and AFL-CIO officials met for four hours to discuss a possible reunion.

Among the nation's larger unions the 1.3-million-member United Auto Workers is regarded as being the least aggressive in the merger-diversification field. But UAW spokesman Don Stillman calls that a bum rap.

"Bringing in people from different occupations is nothing new to us," Stillman said.

He said his union represents about 100,000 white-collar workers in said outside the auto industry. Currently, he said, the UAW is trying to organize 4,000 Blue Cross-Blue Shield workers in Michigan. Other UAW drives to organize clerical workers are under way at Cornell University, Harvard Medical School and Yale University, Stillman said.

The UAW also is a former AFL-CIO affilate that has been invited to rejoin the federation.

Some unions, like the 525,000-member Communications Workers of America, are broadening membership bases largely because they happen to be the only union in town.

"The telephone company is the only big business in many places . . . We're your telephone workers. Like the company, we're there.

"If there are people who want to be organized or who are looking for stronger representation than they have, they often come to us," said CWA spokesman Lee M. White.

Some 2,500 New Jersey state workers seeking "stronger representation" joined the CWA last February. The workers were members of the Mercer County Council No. 4-Civil Service Association, whose representatives voted 144 to 67 to affiliate with the telephone workers' union.

Labor's urge to merge has also been prompted by Big Business' penchant for acquisition and diversification. The unions in the affected industries get together "to better counter the growing concentration of economic power" within the corporations, according to a 1978 report written by Charles J. Janus, a former economist in the Bureau of Labor Statistics.

For example, Janus said, the 1978 merger between the 32,886-member Tobacco Workers International Union and the 135,154-member Bakery and Confectionery Workers came about because of "the tendency of tobacco companies to diversify their holdings by expanding into the bakery and confectionery industry."

Increasing Big Business mergers and the growth of what the AFL-CIO calls "union avoidance schemes" have also produced a need for unions to develop more legal and technical expertise, officials said.

"You can't run a good union today without those services; and many of your smaller unions just can't provide those things to their members," said Frank Pollara, special assistant to AFL-CIO President Kirkland. "Many smaller unions have no real alternative to merger," he said.

Still, there are pitfalls.

Union mergers mean integrating leadership and dues structures, altering constitutions and, in the minds of some, sacrificing sentiment and tradition.

Some mergers, like that between the International Brotherhood of Pottery Workers and the Seafarer's International Union of North America in 1976, have come apart over those and related issues.

The 16,000-member Pottery Workers disaffiliated from the 80,000-member Seafarers in January 1978.

But unionists like the CWA's White say their organizations will continue to push for mergers and diversified memberships.

"It's good protection," White said. "The companies aren't putting all of their eggs into one basket. We'd be fools not to follow their example."