With a smiling Al Gore standing behind him, Gerald McEntee, president of the American Federation of State, County and Municipal Employees, wound up his speech to the union workers gathered here with a rousing call to action.

"Iowa labor is coming, Iowa labor is coming, and if you aren't with us, you better get the hell out of the way."

The audience broke out in wild cheering, and McEntee kept it up: "Sisters and brothers, we neeeeed this man. We neeeeed this man. We don't want to go back to the days of Reagan and Bush."

In the Democratic battle between Gore and Bill Bradley, organized labor is the 800-pound gorilla. It is a force that flexed its muscles two years ago and put underdog Tom Vilsack into the governor's mansion. "If it wasn't for labor, I'd be practicing law right now. I'd have gotten smoked," Vilsack said in a recent interview.

Now, the resurgent union movement under the leadership of AFL-CIO President John Sweeney has its best chance in the early contests to affirm Gore's status as the frontrunner. Its problem here is that the 800-pound gorilla has one arm tied behind its back.

Both the United Auto Workers and the Teamsters have opted out of the primary contest. They have not only declined to follow the endorsement of the AFL-CIO, but told the organization's political operation that it should not include Teamster or UAW members in phone bank lists and other get-out-the-vote efforts. The two unions are adamantly opposed to the Clinton-Gore administration's free trade policies.

The Bradley campaign, in the meantime, is pumping up the strength of labor here in a backhanded way of lowering expectations for the former New Jersey senator.

"You get 20,000 'ones' from labor," Dan Lucas, Bradley's Iowa director, contended, using a code system in which a "one" is a sure vote. With a total of about 80,000 men and women expected to participate in the Democratic caucus, Lucas's estimate would suggest that labor has the power to give fully one quarter of the vote to the candidate of its choice. Gore supporters dismiss Lucas's claims.

While the numbers labor will produce for Gore on Monday night are debatable, there is no question that labor is still the single most important interest group for Democratic candidates in this state. There has not been a competitive Democratic presidential caucus here since 1988, and many of the other politically active groups have let their get-out-the-vote skills atrophy. In addition to making 30,000 telephone calls on Gore's behalf, the Iowa Labor Federation sent mailings to all 150,000 union households in the state.