The effectiveness of organized labor's support for Walter Mondale is on the line Saturday, when Michigan Democrats put aside St. Patrick's Day celebrations long enough to express presidential preferences in caucuses.
''This is the first real test for us and the real test for unions,'' a Mondale campaign adviser says.
Labor is mounting its strongest campaign of 1984 to help its endorsed candidate regain political momentum. Union members must ''work our hearts out'' if Mr. Mondale is to win the Democratic nomination, says
Gerald W. McEntee, president of the American Federation of State, County, and Municipal Employees.
AFL-CIO was ''disappointed'' when Gary Hart scored upset victories in New England and, on Super Tuesday, in Massachusetts, Rhode Island, and Florida - where labor had sought support for Mondale. AFL-CIO took heart when its candidate won primaries in Alabama and Georgia. It considers the victories in the deep South an important turnaround.
Michigan is the second-most unionized state in the nation. (Only New York is more strongly unionized.) Unions represent 850,000 workers, 37 percent of Michigan's nonagricultural work force. Union members are expected to influence the voting of family and friends, so labor's influence may be much larger than figures show.
Paul Jensen, Mondale's labor adviser, talks of organized labor in Michigan as ''a major political power.''
The United Auto Workers, perhaps the biggest power in Michigan labor, represents 350,000 workers. The UAW is a staunch Mondale supporter. According to Franklin D. Garrison, executive director of UAW's political operations, the union hopes ''at least 100,000'' will show up at caucuses to cast votes for Mondale.
If Mondale wins impressively, the results could affect the Illinois primary on Tuesday. Illinois is also strongly unionized. On the same day, caucuses will be held in Minnesota, Mondale's home state.
Victories in Michigan, Illinois, and Minnesota would restore to Mondale the front-runner status, a position critical to his success in New York, Pennsylvania, and other states that are labor-oriented and have large numbers of delegates to July's nominating convention.