Zine Abidine Ben Ali, a 51-year-old army general serving as premier, took over the presidency of Tunisia smoothly and peacefully Saturday after removing an aging President Habib Bourguiba at dawn from the nearly absolute power he had held for 31 years.

Citing a report by a medical commission that the octogenarian Bourguiba was senile and ill, Ben Ali, appointed premier by Bourguiba only a month ago, announced to the nation that the politician who had led Tunisia to independence in 1956 was “absolutely incapable of assuming the duties of president of the republic.”

A few hours later, Ben Ali was sworn in before Parliament as the new president of Tunisia. The Tunisian constitution provides for the premier to succeed to the presidency upon the death, resignation or physical incapacity of the president, but it lays down no rules for determining that incapacity.

Medical Commission Named

Ben Ali solved that problem by quietly appointing a medical commission of prominent doctors to examine the health of Bourguiba, who is officially listed as 84 but may be a year or more older. The commission issued its report at 6 a.m. Saturday, and Ben Ali announced the removal of Bourguiba half an hour later.

This bloodless, constitutional coup, which evidently met no resistance, ended a historic era in which Bourguiba, a nationalist lawyer educated in France, led the North African colony of Tunisia to independence from France and then won international recognition as one of the most pro-Western and reformist leaders in the Arab world. But his reign deteriorated in recent years into autocratic, imperious and erratic rule. He engineered his election as “president for life” in 1974.

It was not clear where the new regime was keeping Bourguiba after his removal from office. Troops had surrounded the presidential palace near Carthage just outside Tunis after midnight Friday. The president, who had been photographed with Ben Ali at a meeting in the palace Friday morning, was believed still there when the troops came. While the troops and an armored car remained on guard Saturday evening, diplomatic sources said they believed that he had been taken to another of his homes elsewhere in the country.

Regime Won’t Look Back

Although Ben Ali treated Bourguiba with some respect in his address to the nation, praising him for his “enormous sacrifices” in liberating and developing Tunisia, it was clear that the new regime does not intend to look back.

Government television, for example, devoted its main evening news almost entirely to the day’s activities and life story of Ben Ali. Hardly a word was said about what Bourguiba had done in the past.

Moreover, although the new Cabinet of President Ben Ali kept many holdovers from the old Bourguiba Cabinet, two of Bourguiba’s closest associates were dropped. There were news reports, in fact, that they and Bourguiba’s presidential secretary were under house arrest.

Many analysts believe that the takeover by Ben Ali was popular, especially in the capital city of Tunis, but there were no mass demonstrations in the streets. People held up extra editions of Tunisian newspapers announcing the change in stark black and red headlines. Many people also gathered at the Ministry of Interior building downtown to try to catch a glimpse of Ben Ali.

Kept Old Interior Post

When appointed premier, he had kept his old post of interior minister, and many of the momentous day’s activities, including the official delivery of the report of the medical commission, evidently took place in his offices in the Ministry of Interior.

At first glance, many analysts do not see Ben Ali, a thick, powerful-looking man, as a sweeping reformer. He has retained many of the Cabinet technocrats from the Bourguiba regime and is looked on, much like his predecessor, as pro-Western. He received his military training at the St. Cyr military academy in France and has taken courses in security and intelligence and in anti-aircraft artillery at U.S. military installations.

But, in his first statement to the nation, broadcast all day on radio and television, Ben Ali promised democratic reforms, including constitutional changes that would prevent anyone from ever again being elected “president for life” and would prevent the automatic succession, like his own, of a premier to the presidency without the people making any decision about it.

New Laws on Press, Parties

He also promised, without giving any details, new laws on political parties and the press.

“Our people,” he said, “have attained a level of responsibility and maturity . . . that allows them to bring their constructive contribution to the management of their affairs.” He repeated many of the same sentiments in an address to Parliament later in the day. And government television described his new regime as the beginning of “a new era of democracy.”

Ben Ali’s calls for democracy drew immediate expressions of support from various groups in Tunisian society, including the main legal opposition party, the Movement of Social Democrats.

Although there has long been speculation that any successor to Bourguiba would naturally try to move closer to more nationalist forces in the Arab world, Ben Ali, as minister of the interior, had been in the forefront of the Bourguiba regime’s campaign to break up organizations of Muslim fundamentalists within Tunisia.

Many Western analysts were inclined to take Ben Ali at his word and conclude that he had acted against Bourguiba mainly because his rule had become so erratic.

‘An End to Chaos and Laxity’

“We will act,” said Ben Ali, “to restore the prestige of the state and put an end to chaos and laxity.”

Many Western analysts believe that Bourguiba had become incapable of running the country but was stubbornly resisting any hint that he resign.

“While Bourguiba remains a beloved figure,” said a longtime Western resident of Tunis, “the last time he appeared on television he was in a state of almost idiocy.”

“There had been a lot of talk lately,” said a Western diplomat, “about how poor the president was in health and behavior.”

Bourguiba, for example, announced the appointment of a new ambassador to the United Nations recently and then soon appointed someone else. There also had been rumors, the diplomat said, that Bourguiba was insisting that the Tunisian courts had been too lenient a few months ago in condemning to death only a handful of extreme Muslim fundamentalists; he reportedly wanted to retry some of those who had escaped execution.

No Details on Illness

In their report signed Saturday morning, the seven Tunisian doctors who made up the medical commission assigned to study the physical and mental health of Bourguiba offered no details about his illness. They simply wrote, “After consultation, discussion and evaluation we affirm that his state of health does not permit him any more to exercise the inherent functions of his post.”

Ben Ali, in his announcement that “national duty requires that we declare that he is absolutely incapable” of serving as president, described Bourguiba as suffering from “senility and the aggravation of his state of health.”

Habib Bourguiba’s official birth date is listed as Aug. 3, 1903, but, because of poorly kept birth records in those colonial times, many Tunisians believe he was probably born earlier. As a nationalist lawyer, he was jailed several times by the French colonial administration that looked on him as a dangerous extremist.

Independence in 1956

Bourguiba was premier when Tunisia became independent in 1956. Three years later, when the traditional Bey of Tunisia was deposed, Bourguiba became the only candidate to run for president.

Although Tunisia had some difficult crises during the early years of independence, including three days of battling with great loss of life over France’s refusal to evacuate its naval base in Bizerta in the early 1960s, Bourguiba soon emerged as one of the Third World’s leading champions of cooperation with the Western powers.