Former Iranian premier Shahpour Bakhtiar reappeared in public today for the first since his overthrow by Iranian revolutionaries, presenting himself as the alterantive to what he called the "mess" of the new Islamic regime.

Bakhtiar, the shah's last premier who vanished in Tehran after the revolutionaries seized power, strongly indicated here that he still considers himself the legitimate head of government of Iran.

He compared himself to Charles de Gaulle, who fled into exile in 1940 to continue the struggle against Nazi Germany and its puppets who usurped power in France.

But Bakhtiar told a press conference held here under the strong protection of the French poilice that he does not intend to form a government-in-exile, to create a new political party or to back candidates in the forthcoming elections in Iran for a constituent assembly.

Looking healthy, tanned and lively, the 65-year-old leader refused to say how he had escaped from Iran or where he has been hiding. French official sources said he had been shuttling back and forth between France and Switzerland, making Thonon-les-Bains, a resort town on the French side of Lake Geneva his principal base for the past new months.

Bakhtiar's reemergence into public view coincides with a French government analysis that the regime of Ayatollah Ruhollah Khomeini is in serious, perhaps irreversible difficulty. Khomeini spent the last four months of his 15-year exile directing the struggle against the shah from French soil.

Bakhtiar's press conference was arranged by his son, Guy, a French intelligence service officer. The elder Bakhtiar is married to a Frenchwoman and their four children are French citizens.

"To the extent," said a French spokesman, "that Mr. Bakhtiar does not disturb public order, he may make public statements."

The French have become progressively disillustioned with Khomeini, not only because he has failed to establish a strong government, but also because it has become increasingly clear that the haven France provided for him is not going to garner this country any special consideration in preserving the $11 billion in development contracts with French companies that were in the works when the shah left Tehran.

Bakhtiar said that Khomeini has no central idea behind his revolution. "No political or religious leader can get the country going again," Bakhtiar said. It could take years to end the economic "mess," he said, but he estimated that the might be able to do it in "at least 18 months."

Islam does not furnish a central idea for the revolution said Bakhtiar, because "if after a thousand years, Iran did not manage to become Islamic, it is too late now," His own slogan, said Bakhtiar, repeating it twice is, "The mullahs back to the mosques."

He said that while he is a Moslem, he represents a secular tradition that believes in the separation of mosque and state, in the protection of minorities and that religious figures should enter politics only to fight antireligious laws.

Bakhtiar appeared to blame Karim Sanjabi, the official leader of Bakhtiar's National Front Party and the Khomeini government's first foreign minister, for creating confusion over Khomeini's true intentions.

"I have left Mr. Sanjabi, and I think that we will never see each other again," Bakhtiar said. "He lost on every count.." He accused Sanjabi of changing his mind "every five days."

The dapper formr premier said that, contrary to Khomeini's entourage, no one in the government of the present premier, Mehdi Bazargan, is after his head.

Bakhtiar was far more indulgent toward Bazargan, another former comrade-in-arms of the National Front, than toward Sanjabi.

The ex-premier said that it is pointless for him to criticize the powerlessness of the Bazargan government since Bazargan does it himself all the time. "It is useless for Bazargan to be in charge because he is doing nothing at all," said Bakhtiar.

Other points Bakhtiar made were:

If he returned to power, he would call a new referendum so people could choose between the monarchy and a republic, but this time not "under the threat of Molotov cocktails."

He, Bakhtair, has had no contacts, direct or indirect with the Shah since leaving Iran, and he had devoted his whole political career to fighting the Shah's government.

"Of course," he is still in touch with his supporters inside Iran. His own 800,000 strong Bakhtiari tribe, centered south of Tehran," could not be anything but sympathetic" to him. It was widely assumed that Bakhtiar's first refuge was mong the Bakhtiaris.

The Sha's executed former premier Amir Abbas Hoveyda was "a great criminal," but he had the right to real trial. "Hovejda was not executed, he was put to death without being tried." CAPTION: Picture, SHAHPOUR BAKHTIAR . . . compares himself to De Gaulle