Shah Mohammad Reza Pahlavi's chances of maintaining the appearance of an orderly departure abroad faded today as Iranian Army soldiers openly fraternized with demonstrators who shouted "death to the shah."

The conduct of the army -- long considered the shah's firmest pillar of support and the last loyal institution in Iran -- dramatized the unraveling of official authority even as the monarch sought to preserve its facade by remaining in the country until Prime Minister Shahpour Bakhtiar's government is formally approved in parliament.

Peaceful crowds, large and small, marched unchallenged through Tehran without sign of army displeasure despite the martial law ban on public gatherings technically still in effect. Demonstrators stuck carnations down the barrels of soldiers' rifles and machine guns. Some troops riding in trucks were seen displaying color portraits of Ayatollah Ruhollah Khomeini, the shah's exiled archenemy and symbol of the campaign to drive him from the throne.

At the Justice Ministry, families of political prisoners demanding unconditional release of their relatives staged an overnight sit-in after several thousand of their supporters occupied the building in yet another sign of public disregard for Bakhtiar's attempts to affirm the authority of his government.

As demonstrators and soldiers smiled at one another in the streets, Bakhtiar told journalists at the lower house of parliament, "I won't be swept away -- I'm too heavy to be swept away."

Bogged down in parliamentary speeches preceding a vote on accepting his Cabinet that is still apparently days away, Bakhtiar sought to minimize the impact of Khomeini's recent political offensive.

From his exile in France, Khomeini yesterday announced establishment of a provisional Islamic Revolutionary Council, which he intimated would sweep the Bakhtiar government away and lead to establishment of the Islamic republic with which he wants to replace the monarchy.

The shah's departure for a foreign vacation, and perhaps permanent exile, is now taken so much for granted that the parliamentary procedure seemed increasingly beside the point. The vote on the Cabinet in both houses of parliament -- presumed to be the final formality before the shah leaves -- is expected Tuesday at the earliest.

[The mayor of Beverly Hills, Calif., Joe Tilem, said after a private conference with a U.S. State Department official that the shah has no plans to seek refuge at the home of his sister in Beverly Hills, as some speculation suggested, The Associated Press reported.]

While the Iranian man in the street is convinced Khomeini will end his 15-year exile as soon as the shah leaves the country, the opposition leadership believes he may hesitate because his return now would risk provoking an army coup d'etat.

In fact, that very fear may then prove Bakhtiar's strongest card. Most observers are convinced, however, that the shah's insistence on respecting protocol already has seriously compromised the government's chances and allowed Khomeini to steal away the initiative.

But Ayatollah Mahmed Taleghani, considered one of Khomeini's closest associates here, told reporters today that the exiled Moslem clergyman would not return to Iran until the shah's rule is formally ended and the recently appointed Regency Council gives way to a Khomeini-sponsored body.

Whether the day's fraternization with the troops was spontaneous or reflected execution of Khomeini's orders to avoid clashes with the army was not clear. But the year-old crisis has seriously strained the army's loyalty to the crown. There is speculation that once the shah does leave the country, draftees especially will be even more open to Khomeini's call for disobedience.

Karim Sanjabi, leader of the National Front political opposition, contends that his supposed allies in France had not consulted him before announcing the Islamic Revolutionary Council.

Clearly embarrassed by Khomeini's acting alone, Sanjabi predicted that demonstrations will continue after the monarch departs, but said the National Front plans "not to say anything on the matter until the shah is gone."

The message from both army and opposition seemed to be that his was a government without enough authority, especially since it would rule under the Regency Council representing the shah.

"A council which has been selected and appointed by the shah cannot have any stronger position than the shah now has himself," Sanjabi told reporters this afternoon, emphasizing this point.