Abol Hassan Bani-Sadr's sardonic half-smile illustrates his own realization that serving as acting foreign minister these days could well jeopardize his wider ambitions. Catapulted into the front ranks by the latest lurch in Iran's revolution, he is stuck with solving the U.S. Embassy hostages crisis, which began with the removal of his rivals from power.

Western observers here have concluded that the hostages' best chances for survival ride on the erratic maneuvering of the French-educated intellectual, who today abruptly scheduled and then unscheduled a trip to the United Nations while helping nurture probes for a deal that could result in freeing the 49 Americans in the U.S. Embassy in Tehran.

Wiser to the outside world than many of his fellow Revolutionary Council members, after spending 15 years exiled in France, Bani-Sadr wants to end the hostage crisis in order to lunch a full-fledged campaign to remove the many vestiges of American influence from his country.

Acting foreign minister only for the duration of the crisis, his is the economics and finance minister in charge of eight ministries dealing with revolutionizing Iran's economic life.

A tireless writer of books, pamphlets and magazine and newspaper articles for many years of exile, he has proved himself adept at radio and television, especially since the U.S. Embasy takeover by radical Islamic students. His relationship with those students continues to be ambiguous to outsiders and, perhaps, to Bani-Sadr and the students as well.

Bani-Sadr's ceaselessly repeated message is simple. Iran must obtain national independence in all spheres. Its economy must be so self-sufficient that prosperity is ensured even without the the oil revenues that account for practically all its foreign exhange earnings.

That was scarcely good news for Iran's bazaar merchants, who supported the revolution in hopes of going back to the good old days of massive imports, but without the competition from supermarkets and easy bank credits that had hurt them in the shah's final years.

Bani-Sdar is a Moslem believer in "small is beautiful." As such, he was no friend of the West, which desperately wants to keep on selling anything from weapons and food to nuclear power plants and cars to pay for its mounting oil import bill.

Part and parcell of BaniSadr's thinking is a deep-seated suspicion of the superpowers and a determination to diminish their influence not only in Iran, but throughout the Third World, to the advantage of Western Europe and Japan.

If the United States is the chief whipping boy now, it is not just because anti-Americanism has helped advance his political career. He lays at America's door the degradation of Iranian cultural, economic and social life wrought since Washington became the paramount influence in Iran in the early 1950s.

Nor has he ever hidden his distaste for communism, especially the Soviet brand, which he, like many other Iranian nationalists, holds responsible for annexing Transcaucasion provinces in the 19th century and occupying northern Iran twice in this century.

Much of his more modern thinking stems from the influence of the late general Charles de Gaulle on Third World intellectuals in the early 1960s when France, freshly free of its colonial burden in Algeria, posed an alternative to the hegemony of the dangerously insensitive superpowers.

A French friend who visited him in his home in a southern Paris suburb during his exile recalled the volumes of Lenin and Mao on the bookshelves and sighed: "When I went to see him I felt 15 years younger. He had remained the perfect leftist student of the early 60s."

Bani-Sadr was influenced greatly by French Iranologist Paul Vielle, with whom he worked for many years while earning has living researching of Iranian society Research Center. Their most influential joint work was a book called "Oil and Violence," on using oil as a political weapon.

Born to the family of an ayatollah in Hamadan Province west of Tehran, Bani-Sadr first studied theology, then turned to economics at Tehran University. When Ayatollah Ruhollah Khomeini was arrested in 1963 for leading anti-American riots, a friendly professor arranged for Bani-Sadr to go to France. When Khomeini spent four months in late 1978 at suburban Neauphle-le-Chateau outside Paris, Bani-Sadr served as an occasional press spokesman.

Rebuffed in his early efforts after the revolution to have banks and industry nationalized, by July he achieved those goals when he was brought formally into the government as deputy finance and economy minister.

He also became editor-in-chief of the newspaper Islamic Revolution, which is a forceful mouthpiece for his ideas.

A combination of charm, timidity and bulldog-like determination, Bani-Sadr can be disarming, whether dealing with foreign diplomats, haranguing a crowd or talking to journalists.

Recently, for example, he received three foreign correspondents late at night in his living room full of friends and family. Curled up on a comfortable armchair in his baggy pants he played with his sockless toes and, between two yawns, matter-of-factly announced that he had ordered Iran to accept no more dollars in payment for oil exports.

That was the first time an oil-producing nation actually had dared to carry out a greatly controversial policy that could weaken the dollar long after the current hostage crisis is solved.