The date Feb. 7 may not mean anything special to most Americans, but it's a big day on Panama's political calendar.

That's when Panamanian presidential hopefuls must declare their candidacy for the May 7 national elections. And this year it may be an important indicator of how much longer Panama will have to endure strongman Manuel Antonio Noriega, who, by controlling more than one president, has ruled the country since Gen. Omar Torrijos' death.Noriega has been indicted on drug trafficking charges by U.S. federal grand juries, and removing him from power has been a foreign policy priority of the Reagan administration.

Noriega hasn't said yet whether he plans to run himself. But he has no shortage of men willing to serve as puppets, and, despite Reagan's efforts to get rid of him, he does not appear ready to voluntarily relinquish power.

The four major opposition parties have announced encouraging plans to run a coalition presidential ticket. The Civic Crusade, the organization that formerly led the opposition, has pledged its backing.

But the parties haven't settled on their standard bearer. Ricardo Arias Calderon looks most likely, but others also are interested.

Noriega doubtless is hoping to divide the opposition and encourage abstention. Conditions are on his side. Nearly all of the opposition media are closed; opposition leaders are frequently jailed or deported; and their businesses are confiscated.

But conditions can be deceiving, as Mexican and Chilean voters learned in the past six months. They too started with divided opposition parties and entrenched governments that appeared firmly in control of the country and the electoral process.

In both places, voters discovered that startling electoral strength can burst forth when government opponents unite.

Panamanians, like Mexicans and Chileans, have the power to change their government. They must do it themselves. The U.S. would only make things worse by interfering. But change it they can, if they will.

By declaring a coalition, government opponents have taken the first step. Now they must follow through and give voters one strong opposition candidate. It is not just the best way to defeat a dictator. In this case it is the only way.