Peace does not come easily in Northern Ireland. But a key vote among the Ulster Unionist party tomorrow will determine whether the region will take a leap closer toward that goal.

David Trimble, leader of the Ulster Unionists and Nobel Peace Prize winner, has been vigorously urging his party's ruling council to vote in favor of returning to governmental power-sharing with Sinn Fein, the political wing of the Irish Republican Army (I.R.A.). Such a vote would be a notable landmark in what has been a long and arduous peace process.

There are dangers that the party's vote might not pass. Earlier this month, the I.R.A. agreed to allow international inspectors access to their secret arsenals of weapons, stopping short of any commitment of disarmament. However, recent proposals about politically charged symbols--such as the name of the province's peace force and the type of flag that will fly over government buildings--have inflamed passions on both sides.

Also, many Unionists have viewed the I.R.A.'s arms concession as an attempt to wriggle out of yet another peace agreement. In February, the I.R.A. had agreed to partial disarmament in return for the continuation and furthering of the independence of Ireland. However, after refusing to begin disarming, the British government resumed rule of Ireland.

Trimble is well aware that the vote is crucial and he has done an admirable job of keeping both sides at the negotiating table. Indeed, it was his decision to delay the vote, originally scheduled for last Saturday, so that he could spend this past week lobbying his party's leaders. In the interests of peace, it would be best for Ulster Unionists to vote for a power-sharing government. The arms inspections signify a turning point in the I.R.A's attitude toward peace, but it is unlikely such an attitude will last long without significant political reforms. And since the situation has been precarious for such a long period, it would behoove the Unionists to accept the I.R.A's gesture as a starting point. A long-lasting peace in Ireland will require firm trust on both sides.