ALL THE PRESIDENT'S HORSES and all the President's men couldn't keep the Senate from being Democratic again. Nothing about the return of a Democratic majority in the Senate is more satisfying than the personal repudiation of Ronald Reagan that it signals. The President raised $33 million and made 23 trips to 15 states to try to stop the Democratic resurgence. But, like Humpty Dumpty, he had a great fall.

Apart from Reagan's loss of face, there seems little reason to be particularly satisfied about the prospects for a resurgence of the Democratic Party. The Democrats did not triumph because they were able to generate a set of issues or to provide an alternative agenda. Their eight-seat gain in the Senate came from a string of races that were decided on local issues. In almost every tightly contested state the local hero won. The outcome Tuesday certainly demonstrated that the voters' newfound attachment to the Grand Old Party may run only as deep as their attachment to Reagan's popularity--and without his name on the ballot, they are far from willing to endorse the kind of policies he has promulgated.

Meanwhile in the statehouses, the Republicans closed from a 34-16 deficit to a 26-24 margin and almost reclaimed the majority of governorships. That's a stunning indicator of the weakness of any supposed Democratic resurgence--and a reminder that the party may have less to cheer about than it thinks.

The challenge for the Democratic Party lies ahead. There has been no political "realignment" yet. Nevertheless, the party balance is clearly at stake going into the 1988 presidential election with few clear favorites for either party. The Republicans have to show that they can win without Reagan by offering the voters something other than the telegenic truisms of the Gipper. The Democrats, on the other hand, should use these encouraging election results to find the resolve to avoid slipping into centrist defeatism. They must reaffirm their commitment to social justice and compassion, to peace and to an activist government ready, willing and able to help.