FEW labor stories in the last decade have ended as happily as last week's elections in America's biggest blue-collar union, the International Brotherhood of Teamsters.New York reformer Ron Carey's upset victory over the old Teamsters leadership shatters traditional stereotypes about membership acceptance of union corruption and opens the way for the Teamsters to play a leading role in revitalizing all of organized labor. For the first time since dissidents toppled the dictatorial regime of W. A. (Tony) Boyle in the United Mine Workers (UMW) 20 years ago, local union activists with no previous role in national union politics or administration will assume control of a major labor organization. Like the UMW under Mr. Boyle, the Teamsters union has been in decline for years. Its endless scandals and notorious reputation became an albatross around the neck of even honest trade unionists, inside or outside the union. Meanwhile, enemies of labor have benefited greatly from all the bad publicity generated by Teamster wrongdoing. Now, however, Teamsters participating in the union's first democratic vote on top officers and executive board members have chosen rank-and-file reformers to clean up and run the union. The union's new president, Mr. Carey, is a former United Parcel Service driver who campaigned relentlessly on a platform calling for greater union accountability and membership empowerment. Given little chance of success at first, Carey and his supporters in Teamsters for a Democratic Union (TDU), a national reform organization, organized a grass-roots revolt similar to those that triumphed over unpopular rulers in Eastern Europe or the former USSR. Like one-time dissidents who now hold power there, the new Teamsters leaders inherit staggering internal and external problems that must be addressed quickly before disillusionment and demoralization set in, leading to a return of the old guard or further unraveling of the organization itself. Foremost among these challenges is the steady drop in membership that has eroded the Teamsters' workplace and political clout. Deregulation, corporate restructuring, and management resistance to new organizing have produced many recent bargaining setbacks in traditional Teamster jurisdictions like trucking and warehousing. To win stronger contracts, conduct successful strikes, and replace the estimated half-million dues-payers it has lost in the last 15 years, the Teamsters union must introduce systemati c worker education and mobilization strategies. Models of more effective unionism already exist within the Teamsters in those locals where TDU has long been active and in other AFL-CIO unions that are trying to maintain membership and momentum by involving the rank-and-file in contract negotiation and recruitment. As these activist unions have discovered, defending workers' rights and benefits in the Reagan-Bush era also requires building strong coalitions with the civil rights, citizen action, environmental, consumer protection, and feminist movements. Long isolated from progressive organizations, a cleansed Teamsters union should be a powerful ally of groups like Jobs With Justice, a community-labor alliance working for national health insurance and new federal budget priorities. For almost a quarter century, the Teamsters union has backed Republican presidential candidates opposed to labor's entire legislative agenda. Teamster members, along with many other workers, have suffered greatly from this self-defeating practice - and President-elect Carey has pledged to change it. As in the reformed UMW, more rank-and-file control over union political contributions and endorsements will send a clear message to would-be recipients of Teamster largesse: Only real "friends of labor" need apply. These and other exciting possibilities created by Carey's victory can be fully exploited only if the Teamsters who elected him remain an active, informed, and organized force within the union. The very low turnout in the union's first referendum vote suggests there is widespread apathy and alienation within the membership. Overcoming this historical legacy of worker exclusion from key decision-making will be no easier in the Teamsters than it is in former communist societies, where much of the citizenry is now free but remains frustrated, depoliticized, and financially battered. New national officers and more democracy will not be enough to transform the union if too many Teamsters sit back and wait for someone else to deliver on Carey's campaign promises. The long-term success of Teamster reform depends on continued bottom-up organizing by the thousands of local union activists who helped lay the groundwork for this week's dramatic changes in the top leadership of the union.