PERHAPS LABOR DAY isn't the most appropriate time to focus attention on the International Brotherhood of Teamsters. Most U.S. workers, after all, are not members of organized labor, and very few of those who do belong to unions have any part in the seamy activities in which many major and minor Teamster officials have been involved over the years. But it's hard to ignore the latest installment in the long romance between the Teamsters and that self-proclaimed bastion of national morality, the Republican Party.

When Vice President George Bush flew to Columbus last Thursday to tell Teamster President Jackie Presser that he and President Reagan are "very, very grateful" for the union's endorsement, he put the finishing touch on a four-year effort to keep Teamster leaders solidly behind the GOP ticket. Those efforts began with the early appointment of Mr. Presser -- who didn't take over the union presidency until last year when his predecessor, Roy Williams was convicted of attempted bribery -- as a senior adviser to the Reagan transition team. President Reagan reinforced his warm feelings toward the union when, only a few days after Mr. Williams' indictment in 1981, he sent a message to the union's convention expressing his hope to be "in team with the Teamsters."

This is not, of course, the first Republican administration to find sufficient points of commonality with the Teamsters to overlook the union's long and sordid history. Richard Nixon's Teamster bonds were, for example, sufficiently strong to prompt union officials to keep contributing hefty amounts to his legal defense until his last day in office. Nor is evidence of the Reagan administration's taste in unions confined to its relations with the Teamsters. Last summer President Reagan decided to become the first U.S. president in history to address a national convention of the International Longshoremen's Association. The luster of the occasion was diminished somewhat by the fact that a number of the union's former top officials could not attend because of previous commitments to be in federal prison.

On policies of major concern to the Teamsters, the administration has delivered as much as the union could reasonably expect. Despite a professed initial commitment to continuing the Carter administration's deregulation of the trucking industry and stiffening labor-racketeering control laws -- both matters opposed by Teamsters leadership -- the Reagan administration has put both on indefinite hold. It is noteworthy that this administration -- which has lectured so self-righteously on the morality of private individuals and commented so scornfully on the Democrat's concern for "special interests" -- has barely troubled to conceal its assiduous concern for one of the most unabashedly self-serving and amoral organized interests in the country.