TUNIS, FEB. 14 -- In his first 100 days in power, Zine Abidine Ben Ali has emerged from the shadowy world of military intelligence and police repression to be hailed here as a political reformer who has pulled Tunisia back from the brink of chaos.

Since he took power from a mentally incapacitated Habib Bourguiba Nov. 7, the new Tunisian president has released 2,000 Islamic fundamentalists and secular political opponents from jail. He has enacted or is preparing laws granting new freedoms to political parties and to the press.

In his first interview since taking power, Ben Ali disclosed last week that he intends to push his liberalization campaign even further in the months to come.

While declining to commit himself at this point, Ben Ali said he is "thinking seriously" about dissolving the Tunisian parliament, which Bourguiba kept as a fief for his Destourian (Constitutional) Socialist Party, and calling elections before they are due in 1991. He also voiced flexibility about commuting the sentence to life imprisonment imposed on Moslem fundamentalist leader Rashid Ghannouchi, whom Bourguiba wanted executed.

The appearance of a sudden conversion to democratic principles and a policy of accommodation toward the Islamic activists whom he repressed severely as Bourguiba's interior minister have added to the image that Tunisians have of Ben Ali as an enigmatic and still undefined figure.

He said that his own reticence, born of his lifelong immersion in the arts of the cloak and the dagger, has contributed to an incorrect view of his own attachment to democracy, which he suggests had to be hidden during the last, disastrous years of Bourguiba.

"I listen. I think. I act. But I don't like to talk. I learned that in the United States," he said, referring to a six-month period of training at the now defunct Senior Intelligence School at Fort Holabird, in Baltimore.

Having attended an American military intelligence school would be a tremendous barrier to a political career in most Third World countries. But Tunisia's new president said that it was excellent preparation for him.

"You learn about analysis, and how to use analysis" in political situations, Ben Ali said without hesitation. He credited his American experience with helping develop the sense of democracy he has shown since gaining power and the sense of stealth he needed to take it.

"When I had to act, I was sure I knew the situation in the country," he said of his move to end the reign of Bourguiba, who he said had become senile and incapable of governing after 30 years as the unchallenged ruler of this North African nation.

Ben Ali, an athletic, compact man of 51, answered questions in crisp and flawless French during a 90-minute interview with Katharine Graham, chairman of The Washington Post Co., and correspondents of The Washington Post and Newsweek conducted Thursday.

Aides said it was the first direct interview with journalists Ben Ali has ever given. He appeared completely at ease answering questions and sipping the juice of Tunisian sweet lemons in the sun-filled dining room of the presidential palace in nearby Carthage.

The interview occurred at a moment when the politically active segments of this Moslem nation of 8 million people continue to voice public support for the reforms Ben Ali has undertaken.

At the same time, they are also asking how far his policies of accommodating the Islamic activists while advancing democratic freedom to the westernized elite that has run Tunisia since independence can go without colliding with each other.

Ben Ali denies that any such collision will occur and suggests that he will fall back on placing clear limits on the fundamentalists if they push too far.

But at present, he leaves the impression that he is working to build a broad political base among moderates that will allow him eventually to run for a popularly mandated term as president. Under the constitution, the term he has assumed expires in 1991.

Libya's Col. Moammar Gadhafi, with whom Ben Ali has restored diplomatic ties and who visited here recently, "thinks I am a great revolutionary" because of the ouster of Bourguiba, Ben Ali said with a smile. "I am a legalist. I work within the system."

Throughout the conversation, Ben Ali emphasized that he had moved with great reluctance against the once-idolized Bourguiba, who guided Tunisia to independence in 1956 and who declared himself president for life in 1975.

Bourguiba, who is at least 84, is under medical care at a villa outside Tunis.

Bourguiba's last days "were impossible. His health did not permit him to govern and everything was blocked," said Ben Ali. "I saw the president every day and I saw what was happening. I had the means and the courage to act. I knew the popular mood. . . . I had my finger on the pulse."

Ben Ali, whose academic training was in electronics and who still enjoys repairing television and radio sets as a hobby, entered military intelligence in the mid-1950s. He says with pride that he soon became the only Tunisian military officer ever to be chosen for the highly specialized course at Fort Holabird.

He left the Tunisian Army more than 15 years ago to devote himself to national security work at Bourguiba's request. Faced with rising discontent, Bourguiba made Ben Ali interior minister in 1986.

Ben Ali's faithful implementation of the harsh crackdowns on Islamic fundamentalists and the secular political opposition in 1987, and his apparent lack of political ambition, persuaded Bourguiba to name him prime minister last October as public demonstrations mounted against Bourguiba's arbitrary and increasingly episodic rule.

Although Ben Ali skirted many of the details, his remarks and accounts from other official sources here establish that Ben Ali and Bourguiba had a climactic argument in late October over the fate of Ghannouchi and other Islamic activists who had been sentenced to life imprisonment on charges of subversion in September.

"Every day he would ask why I had not condemned the fundamentalists yet, and I would have to explain again," Ben Ali said, referring to his refusal to carry out Bourguiba's demands for the staging of new trials that would end in the execution of the fundamentalist leaders.

"He could not distinguish between those who practice religion and those who under the cover of religion, practice subversion," Ben Ali said of Bourguiba, adding later in the interview that he would not make the same mistake. Privately, Ben Ali told a British diplomat as the crisis escalated that executing the Moslem leaders would create martyrs and play into the hands of extremists who had started a sabotage campaign against the government.

Bourguiba was preparing to remove Ben Ali and install as prime minister Mohammed Sayah, a favored courtier who had agreed to carry out the death sentences, when Ben Ali struck first, according to Tunisian sources.

Ben Ali had a panel of seven physicians declare Bourguiba incapacitated under the terms of the constitution and made himself president in the early morning hours of Nov. 7.

"I telephoned Bourguiba between 3:30 a.m. and 4 a.m. to tell him that he would be well treated, that he could have his doctors and nurses look after him, that this was being done in a constitutional manner," Ben Ali said.

"He understood at that time. A few hours later he forgot" the conversation and thought he was still in office, Ben Ali said.

Since leaving the palace, Bourguiba has made only these remarks about the takeover, as reported by Bourguiba's niece to Ben Ali: The new president "should have waited. It would have been his anyway. If he had asked me, I would have given it to him," he reportedly said.

Constitutional amendments being drafted by Ben Ali's government limit any future president to two five-year terms and bar anyone 75 years or older from being a candidate for the office.

The new president outlined a two-stage process he will follow to quell the strong backlash that Bourguiba's campaign against Moslem activists had created.

"First you separate the religious from the political," he said, by allowing legitimate religious activity while outlawing political parties based exclusively on religion. "Then you separate the moderates from the extremists" within the religious movement.

Ben Ali said that "certain advances" made under Bourguiba regarding women's rights would not be sacrificed to accommodate Islamic moderates, but he declined to be specific.

His takeover has also brought a shift in the balance of foreign influence in Tunisia and triggered a more active foreign policy after a period of what Ben Ali called "our absence on the international scene."

The United States, which has maintained close ties to Ben Ali throughout his career, was unusually quick off the mark to welcome the change, while France, the former colonial power and dominant influence here, hesitated.

Tunisia's strong new relations with the United States, which could include increased military cooperation, were hampered only by heavy military debts contracted by Bourguiba and which Ben Ali hopes to persuade Washington to reduce, the president said.

Other Tunisian officials said the military debts, incurred in the purchase of a squadron of F5 jet fighters and M60 tanks, now stand at about $400 million. "This debt is because of Gadhafi," Ben Ali said, referring to U.S. efforts to contain the erratic Libyan leader. "It is now a burden on the economic development of my country."

Ben Ali voiced confidence in his ability to deal with Gadhafi, who mounted subversive campaigns against Tunisia for much of this decade and continues to protest Tunisia's hosting of U.S. Sixth Fleet ships and ranking officials.

Asked if the plan to abolish visas between the two countries by mid-March increased the chances of Libyan subversion, Ben Ali replied:

"We have taken security measures and we will take more if we have to. . . . We are the winners if Libyans come here, because they come to spend money."