The imminent departure of Secretary of State Warren Christopher has been predicted for so long it will be an anti-climax when he actually leaves.

But there now seems little doubt that leave he will, before the end of the year.It's the traditional political remedy. When a president is in trouble, someone's head must roll. President Clinton cannot tolerate much longer the public perception that he has let foreign policy drift.

And Clinton may be waiting for the end of the current congressional term to make his move. Then, and not a moment before, it would be safe to announce the choice of Senate Majority Leader George Mitchell.

The Mitchell scenario is gaining credence, although his current role requires silence about his retirement plans. He is leading the Senate fight for the president's health-care reform. But in the meantime, longtime friendly Democratic activists and foreign policy buffs are lobbying to get him the job.

It may be unfair to blame Christopher for the White House dithering over Haiti and Bosnia and the atmosphere of general indecision on other international issues. But a shake-up at the State Department would send a clear signal that the president finally means to focus on the complicated challenges of the post-Cold War world.

A new Wall Street Journal-NBC Poll indicates that only 34 percent of those surveyed, roughly one third, approve of Clinton's handling of foreign affairs; 54 percent, more than half, disapprove. He does better on his handling of the economy, with 45 percent approval, and his overall approval rating is 49 percent.

The president may be reluctant to dump Christopher in the middle of the controversies over Whitewater and health reform. But soon the re-election campaign will transcend everything. The poll numbers are not good.

Installing a revolving door at State might well add to the impression of a White House that already looks chaotic. But it will be a fleeting problem if the successor is a winner.

Clinton made one stab at revitalizing his diplomatic team last December, when Deputy Secretary Clifton Wharton was forced out in favor of Strobe Talbott, a former journalist and Clinton intimate who had handled Clinton's Russian policy for one year. But not much changed. Russia is a mess. The U.S. role abroad remains as murky as ever.

Christopher has not been a bad secretary. He is respected, intelligent, diplomatic, loyal and discreet. He works hard. His delicate shepherding of the Middle East process has been remarkably successful. In fact, he is said to want to stay until he can lure the last holdout, Syrian President Hafez Assad, to round out the peace by signing a treaty with Israel.

But Christopher lacks the forceful public and private personality necessary to both reassure voters and buck up the president in his weakest area. It is a fatal political flaw.

This does not, heaven forbid, point to another egomaniacal Henry Kissinger, who served in the Nixon and Ford administrations. It is impossible to imagine Clinton tolerating such an aggressive, devious competitor for the limelight. But a happy medium between that and a milque-toast is in order.

Clinton's hesitation about changing secretaries may also reflect the lack of an obvious successor. The foreign policy establishment, which produced a long elite line of Cold War warriors, features few viable stars these days. The dramatic shifting of generations and generational problems worldwide has produced a cacophony of voices and opinions but few leaders and no clear consensus.

Mitchell seems to have what's essential. As majority leader, he is steeped in international issues as well as the domestic politics necessary to support presidential policies. He'd be a cinch for confirmation.