Mourning ceremonies for the victims of last Saturday's Abadan theater fire turned out violent anti-shah demonstrations last night as this southwest Iranian oil town entered what residents said would be a "day of blood."

The feeling against Shah Mohammed Reza Pahlavi and his government - blamed by a majority of townspeople for the tragedy - is open, virulent and overwhelmingly widespread in Abadan, the site of one of the world's largest oil refineries and a key city in the Iranian economy.

Seemingly to a man, residents of this hot, humid town at the head of the Persian Gulf accuse the local police and fire departments of responsibility for the magnitude of the disaster by locking the cinema doors, preventing rescue attempts and displaying sheer incompetence. Many citizens also claim the fire left more than 600 people dead instead of the 377 reported by the government.

At bottom is the message, widely expressed, that after eight months of antigovernment disturbances and frequently violent police responses, in various parts of the country, the only solution to the problem is that the shah must go.

Expressing such a sentiment against the one-man rule of the shah was virtually unthinkable as little as a year ago.

Swarming into the streets last night, the demonstrators in Abadan shouted, "Death to the shah" and "Burn him." As the people coursed through the city there were cries of "We want an end to 50 years of Pahlavi tyranny," a reference to the dynasty started by the shah's father.

"Soldiers you are guiltless, the shah is the real villian," another slogan went.

The police and troops replied by firing tear gas into the mob and bullets over the peoples' heads. Pistol shots and short bursts of automatic weapons fire cracked in the evening air.

The demonstrations started shortly after sundown when thousands of mourners streamed out of the Behbakanian mosque where they had attended ceremonies marking the start of the seventh day after the theater fire. The 7th and 40th days after a death are important mourning times in Islamic custom.

In preparation for the 7th day, local hospitals had stocked up on medical supplies, set aside more beds and otherwise made themselves ready for intense violence.

Many of the mosque-goers marched angrily down the street after the ceremony, shouting their anti-shah slogans. Police wearing gas masks and carrying revolvers raced up other main streets along with truckloads of army troops brandishing American-made M16 automatic rifles with bayonets fixed. They circled the city center and set up roadblocks on streets leading out of it.

After the security forces fired in the air, the demonstrators broke up into groups of about a hundred and took to sidestreets, setting small fires and smashing the windows of banks and any government-associated buildings they could find in the third straight night of such violence.

In one narrow street in a poor quarter, a mob of youths bombarded a bank branch with stones and bricks and heaved trash barrels through its windows. Mingled with a crash of breaking glass was the mournful cry of a Muezzin (a moslem prayer-caller) wailing, Allah Akbars (God is geat).

Children handed me spent bullets, and a middle-aged man brandished an empty U.S. made teargas canister.

"There's just one thing we want to say," he shouted. "We are against the Shah, all of us."

When I tried to leave the area in a packed car, police and soldiers at a roadblock forced the passengers out at gunpoint and searched us closely.

Street rumor had it that four people were killed by gunfire from police and troops, but this was impossible to confirm.

It was clear that what started out as a religious event tonight had quickly turned political. Indeed, the political and religious feelings against the government are intermingled.

One bystander said the rioters were devout Moslems, Communists and rightist nationalists.

The anti-shah tenor of the disturbances was illustrated by Abadan's leading religious figure, Ayatollah Mohammed Kazen Dehdachdi. In an interview he said, "The majority of the people are against the shah. The shah has to go. That's the only thing that will satisfy the people."

The lean- white-bearded Moslem leader said the present disturbances in Abadan were unleashed by the local authorities' handling of the theater fire last weekend.

"We don't know the cause of the disaster, but the one certain thing is that the police prevented people from escaping and locked the doors," he said.

The oft-repeated version going around is that the local police chief, Gen. Reza Razmi, had ordered his men to lock the doors of cinemas during performances following arson and window-breaking at two theaters the previous week. His reasoning was reportedly that no arsonists would be able to break in after a film started, and any already inside would be trapped until firemen quickly arrived to put out the flames.

Razmi was police chief in the holy city of Qom when policemen opened fire on religious demonstrators there in January, starting the cycle of violence that has gripped Iran ever since. The government has called him to Tehran for questioning following the Abadan fire, and some residents have threatened to kill him if he ever returns.