The man on the spot in troubled Tunisia is a cautious, soft-spoken, French-educated lawyer-banker named Hedi Nouira.

He has been prime minister since 1970 and is the constitutionally designated successor to the ailing president for life, Habib Bourguiba. Whether Nouira has built enough of a power base to be able to hold the country together when Bourguiba, 74, dies was called into question again in a Cabinet crisis last week.

Six ministers quit or were fired and Bourguiba, now bedridden but still the country's dominant figure as the father of Tunisian independence, was forced to intervene to shore up Nouira's government.

On Dec. 26, the president appointed seven new Cabinet officers, including his son, Habib Bourguiba Jr., and in a radio broadcast reaffirmed his "complete confidence" in Nouira. "In one hour," a Tunis radio commentary said, "the president has put an end to the maneuvers of those who wanted to provoke governmental crisis and to provoke a breach between him and his right arm, Hedi Nouria."

Reports from the Tunisian capital say the crisis began when the minister of the interior, Tahar Belkhoja, was dismissed, apparently because he wanted to moderate the government's get-tough policy of suppressing the labor unrest that has flared into violence throughout Tunisia over the past two months. The other five resigned in protest but Bourguiba supported Nouira and the new government is likely to continue to deal firmly with the 650,000-member General Union of Tunisian Workers.

What would have happened if Nouira were ruling on his own - as he is soon likely to be since Bourguiba's health continues to fail - is a question that raises doubts about the future stability of the North African nation of 6 million people.

Nouria, 66, is widely respected as an administrator and technician, but he is viewed as a lackluster personality. He is a charming and discursive but cautious man, who is most comfortable speaking French. He shows an ill-concealed contempt for what he views as the politics of mob rule.

In a recent interview, he said that lunisia had to be governed with the understanding that its people are excitable Mediterranean types "who often think with their hands instead of their heads." The latter phrase was edited out of the official transcript of the interview, as were others that might be construed as giving offense to anybody.

Nouira studied law at the University of Paris. He returned to Tunisia in 1937 to practice but his involvement with trade union politics as secretary general of the Tunisiam Trade Union Organization and his support for the independence movement brought him into conflict with the French authorities. According to his official biographic sketch, he spent much of the next 14 years in French jails, and at one time was imprisoned with Bourguiba, to whom he has been loyal ever since.

Since his student days he has been involved in the activities of the Neo-Destour, Tunisia's only political party, and is still its secretary general. In the 1950s he was minister of commerce and finance and from 1958 until he became prime minister he was governor of the central bank.

In the interview, given before the Cabinet crisis, Nouria defended the one-party government as the most suitable for Tunisia, which he described as a country on the road to stablity, development and political sophistication but not yet strong enough for the luxury of complete political freedom.

"There is no Arab country that has achieved as much as Tunisia," he said. The country's objective was not to impose rigid party ideology, he said, but to "liberate the individual from social and materal constraints, that, is from ignorance, hunger, illness and most of all from anachronistic customs."

A multiparty system is not necessarily desirable, he declared, saying that it caused only political turmoil in the third and fourth French republicans, in Italy and in "other countries much more developed that Tunisia."

Tunisia's political system, he said, is one of "modern pluralism, the pluralism of interests" if not of organizations, and is any such country "there are always malcontents."

He said any act by a public official is "studied, criticized analyzed and reviewed and public opinion a Tunisa, vven if it not expressed in writing, is enormously important."

But that leaves it up to the government to judge what public opinion really wants and Nowira apparently has that the agitators for more pay and better working conditions are agitators first and public-spirited citizens afterward. One series of damaging protests, he said, had nothing to do with politics or labor issues at all but was the outgrowth of a bar fight among a group of drunks.

He said it was criminal that people who claimed to be advocating better living conditions for the workers should resort to strikes in the schools, and violence in the streets and factories to promote their view.

It was against that background, that vaguely paternalistic view of the government's role as protector of the Tunisian people from their own mistakes, that he sacked his minister of interior.