Abol Hassan Bani-Sadr, who left here 2 1/2 years ago an obscure opposition militant and rose to become the first president of Iran's Islamic republic, today returned to France once again a political refugee.

Within hours of signing a pledge to abstain from all political activities in or from France, the fugitive former president issued a call for Iranians to "join the resistance" against the Islamic fundamentalists who stripped him of all authority last month.

A French Foreign Ministry spokesman said that the 47-year-old economist had gotten off to a "bad start" and made "an error" by talking to the press.

Subsequently, a news conference was canceled after a middle-level Foreign Ministry official visited Bani-Sadr's apartment in the working-class suburb of Cachan to explain agina the restrictions political asylum entails.

Bani-Sadr flew into Evreux Air Force base, about 60 miles west of Paris, at 4:23 a.m. aboard an Iranian Air Force Boeing 707, which had left Tehran last night and overflown Turkey on its way west.

Arriving in the same plane was Masoud Rajavi, the leader of the Islamic-Marxist Mujaheddin-e-Khalq. Recently he has become the fromer president's principal political ally at the head of a well-disciplined and armed party versed in urban guerrilla techniques.

Some accounts suggested that the plane was hijacked, but close observers of Iranian events here said that version appeared designed to diminish the armed forces' responsibility in helping Bani-Sadr escape and thus void Islamic fundamentalists' reprisals against the military.

News service reported from Tehran that government spokesman Behzad Nabavi told state radio that Bani-Sadr had escaped disguised as a woman after shaving off his moustache and his eyebrows.

His version -- and Bani-Sadr's -- agreed that the pilot, Col. Behzad Moesi, engineered the escape by bundling Bani-Sadr and Rajavi aboard the plane. Nabavi said once airborne on a test flight, Moesi headed for the Turkish border, pursued by Phantom fighters once the authorities realized the trick. The Boeing crossed Turkish airspace just ahead of the Phatoms, Nabavi said.

In any event, Bani-Sadr was without his moustache when he arrived in France.

Some members of the crew asked to return to Iran.

The French Foreign Ministry, while rejecting Tehran's demand for Bani-Sadr's extradition, said the aircraft would be returned to Iran.

The presence of both opposition leaders was generally interpreted as an indicatin of the weakness of the Iranian opposition, a political error or both by Frenchmen and foreigners who follow Iranian developments closely.

Bani-Sadr said that despite rumors of his presence in Kurdistan in western Iran, he had stayed in Tehran since going underground June 12.

Well-informed sources said that Bani-Sadr had remained inside a military barracks in Tehran despite Rajavi's insistence today that the former president had stayed in a house controlled by his guerrillas.

Such was Bani-Sadr's supposed popularity with the military, thanks to his frequent presence at the front since the inconclusive war with Iraq broke out last September, that he was considered perfectly safe in their hands in Tehran.

Even had he felt obliged to leave the capital, he was credited with having strong supprters among antifundamentalist elements in Kurdistan and Azerbaijan in the northwest close to the Turkish border.

"Fleeing was his second grave -- and very likely capital -- political error," commented a French analyst who insisted on remaining anonymous.

He said Bani-Sadr's other mistake was his failure to resign as military commander-in-chief and president last spring before the Islamic fundamentalist-dominated national assembly dismissed him, forcing Ayatollah Ruhollah Khomeini, in turn, to disown him.

With a warrant out for his arrest on charges of "high treason," and a revolutionary prosecutor claiming he should be "killed three times," Bani-Sadr apparently had second thoughts about his once-proud boast of remaining in Iran no matter what happened.

Specifically, Bani-Sadr is charged with abusing power, violating the constitution and provoking counter-revolutionary activity. Fundamentalists blame him for the violent street riots that preceded his dismissal as president.

What lies ahead for the French-educated economist, who spent 16 years after 1963 in exile studying possible reforms for his country, is unclear.

But his return came as a considerable surprise to his intimate friends. Few were optimistic enough to suggest that he might yet emulate Khoemeini who in late 1978 launched from another Parish suburb the last and successful stage of his long fight to unseat shah Mohammad Reza Pahlavi. a

The office of the ousted shah's last prime minister, Shahpour Bakhtiar, who also is in exile here, made it clear that he would have no dealings with Bani-Sadr, although the Tehran authorities lost no time in suggesting that the two men would start plotting together to unseat the revolutionary regime.

A symbol of Bani-Sadr's weakness and abiding tolerance -- he was practically alone among revolutionary leaders in opposing the seizure of the U.S. Embassy in November 1979 -- was his account today of efforts to end the cycle of violence in Tehran.

He told reporters that he had proposed to Khomeini to stop opposition bombings and killings in exchange for an end to the fundamentalists' increasing reliance on executions.

Bani-Sadr admitted that the offer had come to nought.

Escorted by riot squads and armed police wearing bulletproof vest, Bani-Sadr drove at midmorning from Evreux to his Cachan home, where his two daughters have been living for some time.

He told reporters, "I will be staying here until the people [of Iran] follow the path of democracy. Claiming that a "maximum" of 15 percent of the electorate voted for his presidential successor, Mohammed Ali Rajai, Bani-Sadr replied, "soon" when asked when he would be return to Iran.

But virtually forbidden to spek publicly -- unlike Bakhtiar, who is not considered a political refugee -- Bani-Sadr may have a long wait on his hands.