When Tunisia celebrated the 26th anniversary of its independence from France late last month, the local newspapers were full of words from the mighty and not so mighty who had cabled their congratulations to the nation's president for life, Habib Bourguiba.

The list of well-wishers ran from Col. Muammar Qaddafi, the Libyan leader who recently switched from threats against Bourguiba to expressions of brotherhood, to such admirers of the president as his consul in Duesseldorf and members of the African Table Tennis Federation.

For Bourguiba's subjects, sweltering through a heat wave with temperatures hovering around 118 degrees in the shade, the real interest in the names of those cabling their president was not in those published but in the important one that was not--that of the president's wife, Wassila, who left Tunisia in an apparent huff April 17 and did not return until Aug. 2.

In the splendid whitewashed villas along the beaches of Hammanet Bay, where the industrialists and politicians gather to escape the summer's scorching heat, as well as in the sidewalk cafes of the capital where the common folk flock for glasses of coffee and sweet tea when the air begins to cool after sunset, no topic is more talked about these days.

The marital troubles of President Bourguiba, the "supreme combatant," as he is officially known in honor of the struggle he led against the French, are considered not just a personal matter but a metaphor for Tunisian politics at large. While the president represents the little man of Tunisia for whom he has always fought, his wife Wassila is identified with Tunis' conservative bourgeoisie.

"In Bourguiba's dispute with Wassila," noted a well-known Tunisian journalist close to the president's family, "lie all the issues in Tunisian politics. The importance of the first family's estrangement is the fact that it precisely reflects the political conflicts that are molding the future of Tunisia after Bourguiba."

Tunisia after Bourguiba is a topic that has been playing for close to two decades, since he first was hospitalized in Europe for a long spell in the late 1960s for what the rumormongers back home were quick to pronounce the effects of a possible stroke, or bad heart or advanced senility. Letter From Tunisia

How wrong those who have counted the president out over the years have been was evident recently as Bourguiba, officially on the eve of his 80th birthday (although there is evidence that he is at least several years older than that), daily met with a string of foreign visitors who ranged from Oman's minister of interior, to the foreign ministers of Saudi Arabia and Algeria, to Ahmed Sekou Toure, the president of Guinea. Diplomats who deal with the president regularly reported him still very much in control of his government despite all rumors to the contrary.

NO AMOUNT of public activity, however, can still the rumors of the political crisis that underlies the controversy surrounding Bourguiba's wife, long considered one of the aging president's most powerful political advisers and a first lady who has never limited her role to the ceremonial.

Officially, Wassila Bourguiba, 71, left Tunis for Europe for reasons of health and had been reported taking cures or having medical examinations in the West German spa of Baden-Baden or a hospital in the Saudi capital of Riyadh.

Ordinary Tunisians, however, insist that her departure was the result of a political dispute, not health problems.

They note that a year ago she openly questioned her husband's succession plans in a startlingly frank interview with the Paris-based, Tunisian-edited news magazine Jeune Afrique.

Under the constitution, the Tunisian prime minister is to assume the post of president upon Bourguiba's death and hold the office until the end of the parliament's five-year term--in the case of the current parliament, 1986.

In her interview with Jeune Afrique last year, Wassila Bourguiba said the age of her husband's governing class had left it out of touch with reality in the country and with no understanding of the young who make up the majority of its population. She also proposed presidential elections 30 days after the death of her husband rather than leaving the presidency to the prime minister.

THE COMMENTS were not only viewed as a public disagreement with her husband, who had orchestrated the writing of the constitution, but as a direct swipe at Prime Minister Mahmoud Mzali. He was long understood to be out of favor with Wassila Bourguiba, who has cultivated her own coterie of ministers.

Although local gossip has suggested many theories about the rift between the president and his wife, the consensus among the politicians and foreign diplomats following events in the palace seems to be that the president's refusal to dump Mzali may have sparked Wassila Bourguiba's departure.

That she is not really sick is taken as a given by observers in this capital on the Mediterranean, near the ruins of ancient Carthage.

"For someone who is supposed to be sick, she certainly has been traveling and entertaining a lot," noted a member of Tunisia's political establishment, pointing out that the president's wife made numerous side trips around European capitals from Baden-Baden and that while having a "medical checkup" in Riyadh, she not only was reported attending royal parties but also meeting with two Saudi princes, the head of the Arab League, Palestine Liberation Organization Chairman Yasser Arafat and the Tunisian foreign minister.

"It is all something of a comic opera," one western ambassador in Tunis said. "Everyone is talking about it, and it is becoming something of an embarrassment to the president."

JUST HOW MUCH of an embarrassment it has been was shown by the fact that Bourguiba sent Mzali to Riyadh in June, reportedly to try to talk his wife into returning home.

Shortly after she spurned that offer, the president conducted a minor Cabinet reshuffle, firing two ministers--one a close collaborater of his wife's--in a move that seemed designed to strengthen Mzali's position. This was quickly interpreted in Tunisia as a slap at the absent first lady.

At the same time, Bourguiba was being seen in the company of another woman, whom he escorted publicly into his Rolls-Royce for a drive home after an official opening of a dam built with Chinese aid. Sources close to the president said the scene was calculated to make his wife jealous, and it promptly fueled new stories that the president was contemplating taking a new wife.

Last month the president dispatched yet another emissary to his wife, again in Baden-Baden, to persuade her to come home. The envoy, Interior Minister Driss Guida, returned to Tunis and announced that Wassila Bourguiba's health was now fine and that she would be returning "soon." It had been expected that she would be back by last month's Republic Day ceremony. When she was not, the talk was that surely she would be back for her husband's birthday, Aug. 3.

A diplomatic source in Washington confirmed that Wassila Bourguiba returned to Tunisia on Aug. 2.

For the Tunisians weathering the dog day afternoons of a rather eventless if scalding summer, Wassila's return or nonreturn had been viewed as the most important question of the year.