How far is President Clinton in the pocket of organized labor these days? More than ever, and even on small matters. Take the plan in the anti-drug bill that came up in the House last week. The idea is to let the Customs Service rotate its agents, temporarily or permanently, to stop the flow of drugs at crucial (but changing) locations on American borders. Customs officials initially endorsed the measure heartily. And why not? It was their idea. Then labor and the White House got involved, and Customs was forced to withdraw its endorsement. Labor's argument was that the rotating of agents violated the collective bargaining agreement between the Treasury Department and the National Treasury Employees Union. The dilemma at the White House was over whom to side with, a constituency group or drug fighters. But it turned out to be not much of a dilemma at all.