"Once is enough," said President Ricardo de la Espriella, explaining why he cannot and would not try to hold onto his job in elections planned for next year, the first popular vote for a president of Panama since 1968.

"I do not envy anyone this position in 1985," he said, sitting in the elegant official residence where storks wander the courtyard only a few blocks from the dilapidated, overcrowded clapboard tenements of downtown. "The problems Panama has--economic, social--won't be resolved in a year or, for that matter, more."

Central America's wars loom just beyond the horizon. Their indirect impact is already felt in the form of declining investment by frightened financiers and dramatically dropping sales of the products that Panama makes or imports from around the world to its Colon Free Zone.

The more direct threat of violence is a constant worry, and fears are growing that the Reagan administration's apparent willingness to resort to military steps will only make matters worse.

De la Espriella and other Panamanians do not expect Nicaragua or Cuba to respond to increased pressure with capitulation or, for that matter, even with conventional warfare, but by sabotage and subversion that would continue to take advantage of the region's painful underdevelopment.

"I say to the United States, 'What are you waiting for?' " said one top Panamanian official of the relative paucity of development assistance to his or other vulnerable countries in the area. "When we're dead, we don't need you to send the coffin."

Panama faces all this, moreover, with a sense that even now almost two years after strongman Omar Torrijos died in a plane crash there is a "vacuum" in the country's leadership, to use de la Espriella's phrase.

For more than a decade Panama's politics were entirely dominated by Torrijos, who commanded its National Guard, and by a single issue, the Canal. With the treaties in effect since October 1979 and Gen. Torrijos gone since the summer of 1981 the country's political institutions often appeared to be seeking, without finding, an issue or a man around whom they could coalesce.

Torrijos' successor as chief of the National Guard, Gen. Ruben Dario Paredes, 49, is clearly preparing to run for the presidency while trying to hold onto the guard as long as possible. It remains the decisive political institution in the country and by virtually everyone's analysis inside and outside the government it will continue in that role for as long as it wants.

A referendum last month changed certain articles of the Constitution giving the military the right to play a direct and coequal role in running the country along with other political institutions. It also made the legislature a directly elected body, but de facto power is expected to remain in the hands of the soldiers as long as they care to keep it.

Draft electoral laws require Paredes to resign several months (the exact number has not yet been decided) before the vote if he is to be a candidate. He announced Saturday he would step down in August.

In a common analysis here, a leftist academic suggested that Paredes was reluctant to resign because "he knows very well that when he leaves he has no power."

The command of the 11,000 troops in the National Guard, the country's only military force, will pass almost certainly to chief of staff Col. Manuel Antonio Noriega, a former intelligence chief known as one of the most inscrutable, ruthless and skillful political maneuverers in the region.

With Washington appearing to consider a civilian president the "democratic" price for increased military and economic aid in this area and with the expectation that Noriega will not want to divide his authority over the guard with a former colleague, the academic guessed that "it doesn't suit the National Guard to have Paredes in the presidency; it doesn't suit Noriega either and it doesn't suit Washington either, dolts though they may be, to have a military man as president."

Such speculation is increasingly commonplace, but as government officials point out, there is virtually no competition despite the existence of at least 16 political parties.

"In my most intimate self, I would prefer not to be a candidate . No president is going to be popular now," said Paredes in an interview. "The people are demanding solutions, answers, that cannot be given."

"In 1984, the military will have had political power for 16 years," he continued. "We want the military out of power, but it can only be with a powerful president, someone who cannot only win, but can lead. Only a strong president can keep the military out of power."